1. Introduction

Vygotsky’s (1978) Socio-Cultural Theory (SCT) is regarded as a major breakthrough in the field of social psychology and as a resultant in education in general and language education in particular given the significant role of sign system in social construction. SCT is based on certain macro principles mainly including developmental analysis of mental program, social basis of human cognition, scaffolding, mediated learning, and ZPD. In Vygotsky’s sense, scaffolding is defined as the “role of teachers and others in supporting the learner’s development and providing support structures to get to that next stage or level” (Raymond, 2000, p.176, as cited in Van Der Stuyf, 2002).

While SCT principles have been implemented as to certain skills of language ability, writing skill seems to have been left intact to some extent. While writing is one of the main and productive skills, as well as a significant requirement for EFL learners. It is the most difficult skill to master because of its difficulties in generating, organizing, and translating ideas into a readable text (Richards & Renandya, 2002). At the same time, writing is often considered as the most difficult skill to be mastered (Hapsari, 2011). Researchers (Ellis, 2003; Skehan 1998) are now in agreement that L2 proficiency, in general, and writing proficiency, in particular, are multi-componential in nature, and that their principal dimensions can be adequately and comprehensively captured by the notions of complexity, accuracy and fluency (CAF; Housen and Kuiken, 2009).

Writing accuracy refers to “the extent to which the language produced conforms to the target language norms” (Skehan & Foster, 1996, p. 232). Accuracy refers to the production of error-free language. It is estimated by considering the percentage of error‐free clauses (Skehan & Foster, 1996; Skehan & Foster, 1999; Yuan & Ellis, 2004) and the percentage of correct use of target features (Crookes, 1989, as cited in Ellis, 2004).

Scaffolding associates peer-and cooperative endeavor but its implementation seems unimaginable in the absence of ZPD measurement and operationalization. Analogous to society, classroom setting is the combination individuals working and cooperating in a community. It is a must and, of course, to some extent more feasible to identify and probably measure one’s ZPD in a bid to offer some kind of compatible education and input. Nevertheless, pure individualization may look at odd with the other principles of SCT, which is strongly in favor of socially-mediated learning and defining learning as movement along the continuum of intra-personal and inter-personal processes. Such a social, cooperative, and collaborative nature of learning and development requires an initiative to measure both I-ZPD along with GW-ZPD such that the expected mediation, scaffolding and inter-personal and intra-personal processes can be compatible and cooperative. Then, the main problem to be addressed is twofold: operationalization of the varieties of ZPD-based instruction (i.e. I-ZPD vs. GW-ZPD), and incorporation of these two varieties in teaching writing skills in relation to the learners’ variables such as their proficiency level in the form of e,g, test scores.

Based on the significance of the two categories of ZDP and writing in EFL contexts on one hand and the undesirable status of the writing performance of Iranian EFL learners (Hasani and Moghadam, 2012) on the other, this very study is rationalized on the following two premises:

-            the interfaces between EFL learners’ writing quality in terms of accuracy and the two types of ZPD-based instructions (i.e. individualized and group-wide)

-            these instructions’ effect on enhancing writing quality (i.e. accuracy) of Iranian EFL learners in terms of learners' types (i.e. low and high scorers).

In order to accomplish these objectives, the present study, focusing first and foremost on measuring each target learner’s I-ZPD and then on their GW-ZPD or average ZPD, and second on the feasibility and application of each ZPD scenarios in developing writing ability of Iranian EFL learners. More specifically, the following main question realized through four minor ones were posed:

1.         Is there any significant difference in the effect of group-wide ZPD-based instruction and individualized ZPD-based instruction on the writing accuracy of Iranian EFL learners in terms of learners' types (low vs. high scorers)?

1.1     Does GW-ZPD-based instruction and I-ZPD-based instruction have different impact on the accuracy of EFL low-scored learners’ writing?

1.2     Minor Q: Does GW-ZPD-based instruction and I-ZPD-based instruction have different impact on the accuracy of EFL high-scored learners’ writing?

1.3     Minor Q: Does GW-ZPD-based instruction have significantly different effect on low scorers compared to high scorers in developing their writing accuracy?

1.4     Minor Q: Does I-ZPD-based instruction have significantly different effect on low scorers compared to high scorers in developing their writing accuracy?

2. Methodology

The research was conducted empirically through the implementation of the pretest-treatment-posttest design. A homogeneous group of 118 undergraduate, intermediate Persian EFL learners of both genders in the age range of 18 to 22 years old majored in Translation Studies from a university in Tehran students was selected based on their performance on their TOEFL ITP. Then, three pre- and post-tests (two writing tests and a ZPD test) were administered in the first and the last sessions, respectively. The two treatment groups were formed randomly to receive two types of ZPD-based instructions (individualized and group-wide). Another ZPD-test was also administered in the sixth session of the treatment in order to study ZPD development of the two treatment groups and give them their most suitable ZPD-based instructions.

Ultimately, comparison was made between the pre- and post-tests’ scores of the two intact writing classes. The learners’ ZPD development was measured before, after and in the mid of treatment using Raven’s Standard Progressive Matrices (SPM; Raven, 1998). Their ZPD development was, indeed, assessed and analyzed on a weekly basis and a monthly basis (three times in the semester -- before, after, and in the mid of treatment) taking the advantage of Kozulin and Garb’s (2002) learning potential score’s (LPS) formula.

To estimate the inter-rater reliability between the two raters, a randomly selected cluster of writing papers, including 28 sets of papers, scored by the two raters. Running Pearson correlations between these score sets indicated that there were significant agreements between the scores of writing accuracy (r (27) = .73, P < .05 representing a large effect size) as provided by the two raters. As a result, the researcher employed the mean of the two scores provided by the two raters as the final score for each participant’s writing performance in terms of their writing complexity, accuracy.

The treatment was applied for two consequent semesters in order to increase the intra-rater reliability of the findings. Running Pearson correlations between the score sets taken from the first and second semester’s participants of the study indicated that there were significant agreements between the two sets of scores of the participants’ writing performance (r (32) = .83, P < .05 representing a large effect size). As a result, the researcher employed the mean of the two sets of scores taken from the participants during the first and the second semesters as the final score for each participant’s writing performance in terms of their writing accuracy.    

3. Results and Discussion

Due to the non-interval nature of the data, all research questions were probed through non-parametric analysis of covariance (ANCOVA) and Friedman’s test.

As to the first and the second minor research questions about the impact of the two types of ZPD-based instructions on the writing accuracy of the low scorers, and the high-scorers, the researchers taking advantage of the criteria proposed by Wigglesworth and Storch (2009) for the measurement of writing accuracy, came up with the following findings:

-            The I-ZPD-based instruction helped the low-scored learners outperform GW-ZPD-based instruction group on the accuracy of writing (+.003 vs. -.136).

-            While the I-ZPD-based instruction acted as a stronger deterrent against writing accuracy of the high-scored learners than the GW-ZPD-based instruction (-.037 vs. -.078).

As to the third and the fourth minor research questions on the effect of the GW-ZPD-based instruction, and the effect of the I-ZPD-based instruction on the writing accuracy of the low scorers compared to high scorers, the respective ANCOVA came up with the following findings:

-            The GW-ZPD-based instruction act as a deterrent against writing accuracy of the low scorers (-.136) and high scorers (-.037) respectively significantly and slightly.

-            And, the I-ZPD-based instruction acted slightly as a deterrent against writing accuracy of the high scorers (-.078) while acting as a very slight developer of writing accuracy of the low scorers (+.003).

As to the main question on the significant difference in the effect of the g-wide ZPD-based instruction and the I-ZPD-based instruction on the writing accuracy of Iranian EFL learners in terms of the learners' levels (i.e., low vs. high scorers), the researcher defined the I-ZPD-based instruction’s positive impacts on the writing accuracy of the low scorers, and the g-wide ZPD-based instruction’s negative impacts on the writing accuracy of the both levels of the learners (more on the low scorers than the high scorers).

4. Conclusion and Implications

In brief, two main conclusions from the above-mentioned discussion were drawn: 1) I-ZPD-based instruction is constructive to the writing accuracy of the low-scored learners. 2) GW-ZPD-based instruction is more destructive to the writing accuracy of the low scorers than the high scorers.

The results of the present study cast new light on the nature of ZPD, highlighting the significant difference between the two ways of its running (i.e. individualized vs. group-wide) and the achievements of the two types of EFL learners (i.e. low scorers vs. high scorers). These findings were in line with the results of the studies conducted by many other researchers on the individualized scaffolding technique of conference writing (e.g. Aljaafreh & Lantolf, 1994; De Guerrero & Villamil, 1996; Nassaji & Swain, 2010) and on the whole-class scaffolding technique of template studied by several other scholars (e.g. Baleghizadeh et al., 2011; and Smit et al.,2013).

This study has significant pedagogical implications. Syllabus designers can apply two types of scaffoldings (used in the two types of ZPD-based instructions; i.e. group-wide and individualized) effective for the writing accuracy of the relevant low- and high-scored EFL learners to textbooks. The merit of these two types of ZPD-based instructions is that they challenge writing accuracy of the two types of EFL learners differently but in their ZPD providing guided free exploration.