The application of zone of proximal development (ZPD), as a major tenet of Vygotsky’s sociocultural theory (SCT, 1978), has recently been invited in the L2 learning/teaching profession. This study mainly examined whether Iranian EFL learners’ interactions in diverse ZPD-activated proximal contexts through the use of storytelling instruction could improve their oral (speaking) proficiency and attitudes towards speaking in ZPD-based learning context. A pretest-posttest quasi-experimental design was used with 60 intermediate EFL participants selected from Asre-no English Language Institute in Iran, after administering the OQPT. Then, the participants were assigned into 2 experimental groups (ZPD-activated equal and unequal groups), and 1 control group, with 20 participants in each group. The students in both experimental groups were exposed to the storytelling-based instruction within different ZPD-activated proximal contexts (equal and unequal), but in the control group the traditional teacher-fronted instruction within a non-ZPD context was conducted. A semistructured interview and a questionnaire were used to assess the participants’ speaking proficiency and attitudes before and after the instruction. The findings from the analysis of covariance and t test suggested that using storytelling instruction within ZPD-activated contexts significantly improved both the participants’ speaking proficiency and their attitudes. Further data analysis of the ZPD participants’ performance indicated that no significant difference between the learners’ speaking proficiency development of equal and unequal peer groups was found. By implication, ZPD-based pair work and storytelling-based instruction, interwoven with each other in a balanced manner, would be highly fruitful in developing EFL learners’ speaking skill and their attitudes.
