The present study was designed to initially test a model of the role of a set of cognitive (namely, aptitude and working memory) and motivational (namely, language learning goals, self-efficacy beliefs and self-regulation strategy use) individual differences variables in writing performance of a group of Iranian undergraduate EFL learners and, subsequently, to identify the possible differences in the writing quality and composing behavior of learners with different individual characteristics. A convenient sample of 125 BA level students of English Language Teaching and Literature from three state universities in Iran took part in the study. As for the data collection procedure, these participants, in various time intervals, wrote an argumentative essay, responded to the composing process scale, completed the aptitude and working memory measures and filled in the questionnaires exploring their motivational propensities, self-efficacy beliefs and self-regulatory strategy use in writing. The collected data were analyzed by using Path Analysis and Multivariate Analysis of Variance (MANOVA). Due to some problems like small sample size and idiosyncratic nature of the data, the model did not give satisfactory fit indexes. However, it was found that cognitive variables were more strongly correlated with the writing competence of the learners than the motivational ones. More specifically, the construct of foreign language aptitude had the highest potential to account for the writing competence of the learners and the learners having different levels of this construct were different from each other in terms of writing quality and composing processes employed while writing.
