Aptitude-Treatment Interaction Effects on EFL Learners’ Gains in Implicit Grammar Knowledge

The area of Individual Differences (IDs) and their interactions with instructional conditions have recently been a point of interest in second language acquisition. However, the effect of such interaction on aural implicit grammar knowledge has not been researched exhaustively. This study thus examined the interactive effects of aptitude and treatment conditions on implicit grammar knowledge as elicited aurally. Grammar knowledge was operationalized as the ability to comprehend past/present simple passive verbs. To this end, 120 EFL learners were randomly assigned to four groups: three teacher-generated experimental (Isolated Form-Focused Instruction, henceforth FFI, Integrated FFI, and Incidental) conditions, each lasting for six treatment sessions, and a control group receiving the same content with no instruction. Initially, learners took a pre-test and cognitive tests (LLAMA-D, LLAMA-F, and LSPAN). They then received the treatments, and three days after the treatments, they took an Aural Timed Grammaticality Judgment Test as a measure of implicit grammar knowledge. Results of a general linear model revealed a significant effect for treatment. Additionally, LSPAN was found to mediate the effectiveness of instruction, with the highest effect on implicit grammar knowledge under the Isolated FFI condition. Post-hoc analyses also demonstrated that instruction made a significant difference compared with no instruction, though, in comparison with other conditions, Integrated FFI proved to be more effective. Results provide EFL teachers and curriculum developers with awareness concerning the interaction between instruction and cognitive differences. For improving the effectiveness of instruction and acquiring implicit knowledge, cognitive tasks, especially those boosting working memory, are suggested.