Psycholinguistics involvement load hypothesis

Richard S Pinner RPinner Psycholinguistics- Involvement Load Hypothesis.docx
12/05/2009

The Involvement-Load Hypothesis:
review and pedagogic implications

Contents

Introduction ............................................................................................................................................ 2

Vocabulary Acquisition in L2 ................................................................................................................ 3

The Involvement-Load Hypothesis ....................................................................................................... 4
Need ................................................................................................................................................. 6
Search ............................................................................................................................................... 6
Evaluation ......................................................................................................................................... 7

Evidence for the Involvement-Load Hypothesis – a summary of research findings ........................ 8

Weighting .............................................................................................................................................. 11

Conclusion ............................................................................................................................................. 14

Bibliography.......................................................................................................................................... 15

Appendix ............................................................................................................................................... 16

Richard Page 1
Originally submitted to King‟s College London as part of an MA in Applied Linguistics and ELT

12/05/2009

Introduction

The challenges faced when learning a second language can be very imposing. One of

the largest obstacles to overcome when attempting to master an L2 is the learning of

vocabulary. Even to have a reasonable command of an L2, the learner may have to

memorise thousands of new words, and learning a word involves much more than just

knowing the semantic reference; such as phonological, syntagmatic and connotational

information (Richards 1974, Nation 2001). Learning vocabulary and building an L2

lexicon takes a long time, a great deal of effort and, presumably a lot of mental

storage space. A tried and tested method of really learning vocabulary and being able

to retain and use it productively would have huge implications across Second

Language Acquisition and ELT. Laufer and Hulstijn proposed the Involvement-Load

Hypothesis (ILH), a “construct of involvement with motivational and cognitive

dimensions” (Laufer & Hulstijn, 2001:1) which was intended to overcome some of

the issues involved in empirically testing involvement. The theory attempts to

operationalize task based involvement by assessing it using three factors; Need,

Search and Evaluation.

In this essay I will briefly examine first the literature that led up-to the proposal of the

Involvement-Load Hypothesis, and in more detail the subsequent empirical research.

The roots of the Involvement-Load Hypothesis have been in existence around

vocabulary teaching for a number of decades, but Laufer and Hulstijn have provided a

theory which can be operationalized and evaluated with a great deal of clarity. I will

discuss the findings of the research around involvement and cognitive processing

around vocabulary acquisition. This is a very new hypothesis within the field and as

such further studies are still needed in order to arrive at solid conclusions, particularly

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in terms of pedagogy and task-design. I will asses the weighting of the three factors

(Need, Search and Evaluation) that make up the Involvement-Load Hypothesis and

the potential problems with the current proposal. Finally I will look briefly at

pedagogical implications for foreign language learners and teachers.

Vocabulary Acquisition in L2

Within learning and teaching foreign languages the need for learning vocabulary has

always been of great importance. It is somewhat easier to explain or understand when

grammar rules are not adhered to, but vocabulary issues prevent understanding as it is

much harder to understand if the wrong word is used (Lightbown & Spada 2006:96 )

In a poll of ESL students at UCLA, “68 percent […] indicated that they considered an

inadequate vocabulary to be the main single contributor to [comprehension]

problems” (Crow and Quigley, 1985:499). It is strange then, that research into

vocabulary acquisition has been marked by a “recurring theme [of] neglect” (Hedge

2000:110). However, recently there is a much greater amount of studies into the way

we learn and acquire words, which has been described as an “explosion of vocabulary

sudies” (Schmitt 1998:282). I think that perhaps now interest and research in L2

vocabulary is at an all time high. There is a host of theories surrounding the

acquisition and retention of L2 vocabulary, for instance the Input Hypothesis

(Krashen 1989) which proposed that exposure to great amounts of vocabulary will

lead to implicit acquisition. Ellis & He (1999) put forward claims about how words

are learned implicitly and explicitly, separating the type of vocabulary knowledge (i.e.

phonetic, orthographic, semantic and syntagmatic). Of particular relevance to the

Involvement-Load Hypothesis is the depth of processing hypothesis, which outlines

“a series or hierarchy of processing stages … referred to as “depth of processing”

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where greater “depth” implies a greater degree of semantic or cognitive analysis”

(Craik & Lockhart, 1972:675). It was argued that the depth at which new information

is processed has more effect on retention and learning than the length of time it is

stored in short-term memory. They pointed out the flaws of approaching vocabulary

acquisition from the perspective of long and short term memory The depth of

processing theory, however, failed to provide enough detail to make it

operationalizable. Laufer and Hulstijn point out that the two problems with the theory

where insufficient detail about “what exactly constitutes a „level‟ of processing”

(Laufer & Hulstijn, 2001:5) and how to measure the supposed depth of any given

level. The theory was expanded on further by Craik and Tulving (1975) but again the

persistent problem in making the factors operationalizable continued to mark the

development of an empirically testable hypothesis.

The Involvement-Load Hypothesis

The Involvement-Load Hypothesis (ILH) was proposed “to stimulate theoretical

thinking and empirical research in the domain of L2 vocabulary learning” (Laufer &

Hulstijn, 2001:1) which I think it has succeeded in doing as there are numerous

studies which were set up specifically to test it (Kim, 2008; Keating 2009; Eckerth &

Tavakoli, forthcoming). In addition, the hypothesis complements other theories about

cognitive processing and retention of vocabulary that have been in existence for

several decades (for example Craik & Lockhart, 1972; Ellis & He, 1999; Robinson

2001). The hypothesis is a way of analysing the cognitive and motivational

involvement of any given L2 vocabulary acquisition task.

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Laufer and Hulstijn defined the hypothesis as “the combination of the presence or

absence of the involvement factors Need, Search and Evaluation.” (ibid: 2001:15)

Each of the involvement factors can be represented as either minus (-) which shows

the factor as not present in a given task, plus (+) indicates a moderate presence of the

factor and a strong presence is represented by a double plus (++). The grades of

strength are explained within the context of each factor, so I shall explain them

individually.

Table 1
(Taken from Laufer & Hulstijn 2001:18)

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Need

This factor is the “motivational, non-cognitive component” (Keating, 2008:366) and

simply refers to the requirement of knowing or understanding the target vocabulary in

order to successfully complete a given task. Laufer and Hulstijn (2001) claimed that a

task-induced Need was moderate (+) and a learner-imposed Need, perhaps due to a

learner wanting to learn or use the word for their own purposes, constitutes a strong

Need (++). In my view, one of the strengths of ILH is that it accounts for the

distinction between Intrinsic and Extrinsic motivation, which is important in theories

conceptualising motivation (Richards & Schmitt 2002:343). Another strength is that

each factor can take into account internal and external factors which are either task-

induced or learner-induced. In the next section I will discuss the weighting of the

factors in more detail, but at this point I wish to draw attention to the fact that the

Involvement-Load Hypothesis places equal weight on each factor as contributing to

involvement load. I believe that Need may be the strongest factor in involvement

load, and my own L2 learning experiences have contributed to this view as I will

outline in the Weighting section.

Search

This is one of the two cognitive components (the other being Evaluation) that

comprise involvement load. As the name suggests, Search outlines the need to look-

up unfamiliar vocabulary. This could be done using a dictionary, but the provision of

a gloss provided within the task itself is considered to be a Search factor absence (-).

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A large number of the studies around ILH have focussed on Search and attempted to

quantify the amount and the effect of looking up the meaning of words in glosses or

dictionaries. Rott (2007) found that glossing and repeating target words “resulted in

more productive word gain” (Ibid, 2007:165) than simply bolding target words or

encountering a target word only once.

Laufer and Hulstijn (2001:21) point out that the weight of “search might be lower

than that of Need and Evaluation.” Again, I will discuss this possibility further in the

next section. In Table 1 Task Induced Involvement load there is no representation of

Search with a strong presence (++) implying it is simply either present in a task or

not, but can not be graded further.

Evaluation

This is the second cognitive factor and also perhaps another heavily weighted aspect.

Evaluation requires the user/learner to engage with the word in terms of deciding

contextual suitability, choice over other synonyms and “entails a comparison of a

given word with other words” (Ibid, 2001:14).

Since the proposal of the Involvement-Load Hypothesis, there have been many

attempts to prove and expand upon the theory, because it is operationalizable based on

the three factors it presents as defining involvement. Evaluation is defined as

moderate in tasks where vocabulary items are matched to homonyms or definitions.

Strong Evaluation is found in a task such as using the word in an original sentence,

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where the word would have to be processed on semantic and syntagmatic levels

involving collocation and contextual appropriacy (Ibid, 2001:15)

In the Evaluation factor, it may prove necessary to have more than three

representations (-, + and ++) of the depth of involvement, as Evaluation is certainly a

complex factor. However, it seems that within the Involvement-Load Hypothesis in

its initial conception each factor was presented to be of equal weight, and the depth of

each level was kept within the realm of absent, moderate or strong for

operationalizable simplicity. However, this may be at the expense of accuracy. For

instance, consider two tasks with strong Evaluation factors (++). In one task the

students are required to write original sentences with target words (See Table 1 task 5,

++). In another task the students are required to write an original essay or composition

of some sort using all the target words, but not necessarily in each sentence (Table 1

tasks 6 and 7, ++). The Evaluation in this second task, I would argue, is much

stronger than the first because the learner must not only select collocational and

contextual appropriacy but also link these sentences into one composition which itself

is applicable overall in those terms. In my view, the composition task seems to

involve an additional level of Evaluation than sentence writing alone, hence future

studies into this factor could prove valuable.

Evidence for the Involvement-Load Hypothesis – a summary

of research findings

Much of the evidence for the hypothesis has seemed to confirm the theory that the

more actively the learner engages with target words, the more likely they are to

acquire and retain those words. For example, Hulstijn et al (1996) investigated the

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effect of Search and also the frequency of occurrence and found that there was a

positive effect on the learners‟ recall of the words.

Peters et al (2009) looked at the effect of vocabulary tasks on word retention. In the

study glosses were provided in the form of a clickable L1 definition and L2 contextual

example which appeared on a computer screen during the reading task when clicked.

The number of look-ups was recorded by the researchers, and there was a definite

correlation between number and frequency of look-ups in intentional learning groups

(given forewarning of a target vocabulary test) and incidental learning groups (not

informed about the upcoming test). I tried this myself in a classroom setting with an

advanced group of learners on a group of intensive EFL students1. I informed them

during a reading task that I would test them on vocabulary and I noticed a much

greater amount2 of look-up activity than on the previous reading activity I had done

with no forewarning. Peters et al reported “robust evidence” (2009:114) that

acquisition is improved by strengthening Search factors (in addition to Evaluation)

and were able to conclude that the effect of enhancement techniques 3 “corroborated

the findings of previous studies” (2009:146) related to task-induced relevance.

More research done specifically in order to test ILH confirmed its validity, while

supplying additional dimensions or pointing out small limitations. Hulstijn & Laufer

(2001) have conducted their own test of ILH. Subjects were assigned into groups,

1
These students are studying English in London so they are immersed in the target culture which
makes them different from the more common EFL context where the students are not immersed in the
culture of the target language.
2
There are some students who regularly use dictionaries and have their own electronic device for
looking up words, however in the class we also keep a number of dictionaries for student use and upon
announcing the test I was instantly asked by the students for these dictionaries, but in the previous
reading task the dictionaries were not requested.
3
These were comprised of Looking up meaning, Elaborately processing and multiplying instances
(repetition) of target words

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each of which completed one of three tasks, each with different involvement loads.

Task 1 was a reading with comprehension questions. It had moderate Need but an

absence of Search and Evaluation, thus giving it an involvement index of 1. Task 2

was the same as Task 1 except the ten target words were deleted from the reading

with an additional gap fill activity which required productive (orthographic recall

only) knowledge of the target words. The involvement index was 2 because there was

moderate Need and Evaluation but no Search. Task 3 was a writing composition

requiring the use of the target words. There was no reading, just the composition and

the index was 3 because it has moderate Need, strong Evaluation and no Search. The

study was carried out in two institutions, one in Israel and one in the Netherlands. The

Hebrew-English group‟s findings were fully in line with ILH, but the data from the

Dutch-English group showed there was not a significant difference between groups

who completed the gap fill (Task 2) and the composition (Task 3) activities. Of

particular relevance to this finding is the study by Keating (2008). He partially

reconstructed4 the test conducted by Hulstijn & Laufer (2001) with the additional

consideration of time on task. Keating again found that Task 3 was not more effective

than Task 2, and with the time on task consideration Task 3 could actually be taken to

be less effective than Task 2. Both studies also featured a post-test to measure the

retention of the words. ILH again proved to have a positive effect on both acquisition

and retention.

Kim (2008) designed a study to test the effect of tasks with the same involvement

load index but differing in the factors that comprised that index. The study revealed

that tasks with the same involvement index produced similar gains in acquisition and
4
This was not a direct reconstruction as there were additional factors taken into account, one being the
level of proficiency. In Hulstijn & Laufer 2001, the learners were advanced, but Keating chose to focus
on lower level proficiency to see if the effects were the same, which they were.

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retention. Kim concluded that further study into the operationalizable factors within

ILH need to be empirically tested.

One key research finding is that the groups who completed gapping or matching

activities were not always significantly outperformed by the original composition

groups. Pedagogically, this is a key finding due to the fact that within the classroom

there are often time constraints, which Keating (2008) evaluated. This is an important

finding and again throws up the limitation that Laufer and Hulstijn (2001) pointed out

with their initial proposal of the theory, that “all three factors may not be equally

important for vocabulary learning” (Laufer & Hulstijn, 2001:21). Although Kim‟s test

of the operationalizable reliability of ILH added support to the hypothesis, there is

still a need for further testing and research. As mentioned in the discussion of the

Need factor, I will look at weighting in more detail in the next section.

Weighting

In terms of research and thus pedagogical applications the Involvement-Load

Hypothesis is highly stable and reliable. This has been proven in the numerous studies

that have been done around vocabulary acquisition, both prior to the hypothesis (Ellis

& He, 1999; Hulstijn et al, 1996; Laufer & Nation, 1999) and subsequent (Rott, 2007;

Webb, 2005; Laufer, 2003, 2006). In addition, direct tests of the hypothesis have

yielded positive results, although the main deviation is in the effectiveness of certain

tasks. For example the gapping task (Table 1, task 4) seems to be similar to the

composition task (Table 1, tasks 6 and 7). However, there have been tests of ILH that

did not corroborate the findings. Martínez-Fernández (2004) reports no difference

between higher depths of processing on vocabulary development. Her study used

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rather different types of task, focussing on incidental and implicit learning and using

think-aloud protocols. She also reported a discrepancy between the factors that

operationalize involvement, particularly Search and Evaluation. However, in

Martínez-Fernández‟s test the participants were told they would have to re-tell the

information from the reading, and thus the focus was on overall comprehension and

not individual vocabulary items. This may account for the data she collected. Rott

(2007) pointed out, and I agree, that pedagogically, tasks like those used in testing

ILH may have a negative effect on global comprehension of the text, which needs to

be considered if combining vocabulary acquisition with reading comprehension in

class.

Another test by Browne (2002) attempted to pitch various hypotheses of vocabulary

acquisition against each other. The study was designed to test the Input Hypothesis

(Krashen 1989) the Involvement-Load Hypothesis (Laufer & Hulstijn 2001) and the

Pushed Output Theory (Swain 1985). Browne claims that “more words were learned”

(2002:1) via the Pushed Output Theory. The flaw in Browne‟s claim is that this theory

was tested by writing words in original sentences which of course does not

differentiate it from ILH.

In my view, ILH is a powerfully persuasive theory because, as Keating (2009) points

out, it fits in well with other studies and theories in the field, for example word

glossing, look-up and frequency (Peters et al 2009) task-induced involvement (Laufer

2003, 2006) and theories around negotiation and interaction (Nation & He, 1999). The

Involvement-Load Hypothesis‟ greatest strength lies in the way it is reliably

operationalized, however, therein also lies a need for further testing and re-evaluation.

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As I mentioned before when outlining the hypothesis, there is perhaps a problem with

the simplified model for calculating involvement index (-, + and ++). The three

factors Need, Search and Evaluation, it could be argued, exist on levels more subtle

than moderate and strong. Because not-present (-) is not a measure but rather an

absence, there are effectively only two strengths at which a factor is indexed (+ and

++). This could be what has led to disparity between tasks such as gapping and

composition, so perhaps a more accurate scale would be absent (0) weak (1),

moderate (2), strong (3) and intense (4).

Another possible limitation that Laufer and Hulstijn present is in the giving of equal

involvement index across all factors. Need in my own L2 studies has always proved

to be the most prevalent factor in acquisition. For example I learned the Japanese

word „tasukete‟ (助けて) which means „help me‟ before learning „tetsudau‟ (手伝う)

meaning „can I help (you?).‟ I needed to request help when using Japanese much

more often than I found myself able to offer it, and it took a lot longer to remember

and be able to recall the latter item. When I learned „tasukete‟ I heard it only once in a

film and deduced the meaning (moderate Evaluation but intense Need). However,

with „tetsudau‟ I had to constantly write, read and be drilled before I could claim

productive knowledge. Another example is how quickly after only one or two

hearings I learned „ouyougengogaku‟ (応用言語学) or „applied linguistics‟ but I have

heard the words for science and history many times and still have trouble

remembering them. From these personal observations I believe (+) Need may be

much stronger than (+) Search and possibly even Evaluation for learners.

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Conclusion

The Involvement-Load Hypothesis has stood up well to empirical testing, proving that

it is reliably operationalizable despite the factors discussed in the previous section. It

also complements other theories and approaches such as Task-Involvement, frequency

of occurrence and Depth of Processing. More ideas and research are being added all

the time, which means that the reliability of the hypothesis will improve. Already, the

pedagogical significance is very clear, and particularly for task-based approaches

(Rodgers, 2001; VanPatten & Williams, 2006). The better we understand what is

involved in learning and retaining words the better we can create materials and tasks

which utilise this knowledge. Already, there are materials which present vocabulary

in a way which is inline with ILH (See Appendix). For this reason every effort should

be put into strengthening the hypothesis, which is still relatively new and yet has

already had a deep and possibly lasting effect on second language vocabulary

instruction.

(3,315 Words)

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Bibliography

Browne, C. (2002). To push or not to push: A Hulstijn, J. H., Hollander, M., & Greidanus, T.
vocabulary research question. Aoyama (1996). Incidental vocabulary learning by
Ronshu, Aoyama Gakuin University Press. advanced foreign language students: The
influence of marginal glosses, dictionary use,
Craik, F. I. M., & Lockhart, R. S. (1972). and reoccurrence of unknown words. The
Levels of processing: A framework for Modern Language Journal, 80, 327–339.
memory research. Journal of Verbal Learning
and Verbal Behavior, 11, 671–684. Keating, G.D. (2008) Task effectiveness and
word learning in a second language: The
Craik, F. I. M., & Tulving, E. (1975). Depth of Involvement-Load Hypothesis on trial
processing and the retention of words in Language Teaching Research 2008; 12; 365
episodic memory. Journal of Experimental
Psychology: General, 104, 268–294. Kim, YouJin (2008) The Role of Task-Induced
Involvement and Learner Proficiency in L2
Crow, J.T. and Quigley, J.R.(1985) A semantic Vocabulary Acquisition Language Learning
field approach to passive vocabulary 58:2, June 2008, pp. 285–325 ISSN 0023-8333
acquisition for reading comprehension TESOL
Quarterly 19/3 Krashen, S. (1989) We acquire vocabulary and
spelling by reading: Additional evidence for
Eckerth, J. & Tavakoli, P. (Forthcoming) the input hypothesis The Modern Language
Effects of Task Induced Involvement and Journal 73: 440-64
Frequency of Exposure on L2 Vocabulary
Acquisition and Text Comprehension. Laufer, B. & Nation, P. (1999) A vocabulary-
size test of controlled productive ability
Ellis, R., & He, X. (1999). The roles of Language Testing 1999 16; 33
modified input and output in the incidental
acquisition of word meanings. Studies in Laufer, B. (1997) What‟s in a word that make
Second Language Acquisition, 21, 285–301. it hard or easy: some intralexical factors that
affect the learning of words in Schmitt, N. &
Hedge, T. (2000) Teaching and Learning in McCarthy, M. (eds) 1997 Vocabulary:
the Language Classroom Oxford: Oxford Description, Acquisition and Pedagogy
University Press
Laufer, B. (2003). Vocabulary acquisition in a
Horst, M., Cobb T., & Meara, P. (1998). second language: Do learners really acquire
Beyond A Clockwork Orange: Acquiring most vocabulary by reading? Some empirical
second language vocabulary through reading. evidence. The Canadian Modern Language
Reading in a Foreign Language,11(2), 207– Review, 59, 567–587.
223.
Laufer, B. (2006). Comparing focus on form
Hulstijn, J. H., & Laufer, B. (2001). Some and focus on form in second-language
empirical evidence for the Involvement-Load vocabulary learning. The Canadian Modern
Hypothesis in vocabulary acquisition. Language Review, 63, 149–166.
Language Learning, 51, 539–558.
Laufer, B., & Hulstijn, J. H. (2001). Incidental
vocabulary acquisition in a second language:
The construct of task-induced involvement.
Applied Linguistics, 22, 1–26.

Laufer, B., & Paribakht, T. S. (1998). The
relationship between passive and active
vocabularies: Effects of language learning
context. Language Learning, 48(3), 365–391.

Lightbown, P.M. & Spada, N. (2006) How
Languages are Learned 3rd Ed Oxford: Oxford
University Press

Richard Page 15

12/05/2009

Rott, S. (2007) The Effect of Frequency of
Martínez-Fernández, A. (2004) Revisiting the Input- Enhancements on Word Learning and
Involvement-Load Hypothesis: Awareness, Text Comprehension Language Learning 57:2,
Type of Task and Type of Item Language June 2007, pp. 165–199 ISSN 0023-8333
Testing 2004; 21; 202
Schmitt, N. (1998). Tracking the incidental
Nation, I. S. P. (2001). Learning vocabulary in acquisition of second language vocabulary: A
another language. Cambridge: Cambridge longitudinal study. Language Learning, 48(2),
University Press. 281–317.

Nation, P. & Coady, J. (1988) Vocabulary and Schmitt, N. (2008) Instructed second language
Reading in Vocabulary and Language vocabulary learning Language Teaching
Teaching Carter, R. & McCarthy, M 1999 Research 2008; 12; 329
Pearson Education
Swain, M. (1985). Communicative
Peters, E. Hulstijn, J. Sercum, L. Lutjeharms, competence: some roles for comprehensible
M. (2009) Learning L2 German Vocabulary input and comprehensible output in its
Through Reading: The Effect of Three development. In S. Gass & C. Madden (eds.)
Enhancement Techniques Compared Input and Second Language Acquisition.
Language Learning 59:1, March 2009, pp. Rowley, MA: Newbury House
113–151 ISSN 0023-8333
VanPatten, B. & Williams, J. (eds) Theories in
Richards, J.C. & Schmidt, R. (2002) Second Language Acquisition: An
Dictionary of Language Teaching and Applied introduction, Routeledge
Linguistics (3rd Edition) Longman; Harlow
Webb, S. (1997) Receptive and productive
Richards, J.C. (1976) The Role of Vocabulary Vocabulary sizes of L2 Learners Studies in
Teaching TESOL Quarterly, Vol. 10, No. 1 Second Language Acquisition, 30, 79–95
(Mar., 1976), pp. 77-89 Cambridge University Press

Robinson, P. (ed) (2001) Cognition and Webb, S. (2005). Receptive and productive
Second Language Instruction Cambridge: vocabulary learning: The effects of reading
Cambridge University Press. and writing on word knowledge. Studies in
Second Language Acquisition, 27, 33–52.

Appendix
The following lessons are taken from www.onestopenglish.com. They are adaptations of articles from
the British newspaper The Guardian and each week there is a new one created.

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After this task there is a reading and comprehension questions. Following that there is a matching
activity. In many of these lessons the vocabulary is not the same as the initial key words, but if it were
the same there would be a higher chance of acquisition.

However, the teacher can easily adapt these materials and have the students produce original sentences
using the target words. To account for time on task in class, this could be set as a homework exercise.

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