The effects of task complexity and language aptitude on EFL learners’ writing performance

The present study investigated the effects of task complexity and language aptitude on upper-intermediate EFL learners’ argumentative writing performance in terms of syntactic complexity, lexical complexity, accuracy and fluency. The findings of this study demonstrated that increasing task complexity manipulated by the number of elements and the degree of reasoning along the resource-directing dimension leads to enhancement of syntactic complexity and lexical diversity, and there are low correlations between language aptitude (mainly number learning and spelling clues) and writing performance. What’s more, task complexity and language aptitude (and its components) are predictors for writing performance in terms of intraclausal level of syntactic complexity, lexical diversity and fluency. These findings lend partial support to the Cognition hypothesis and Aptitude Complexes Hypothesis in L2 writing. Theoretical, methodological, and pedagogical implications of the study for task design and implementation as well as for task-based assessment in language education programs are discussed.