One of the concerns in language testing is measuring the extent to which the same constructs occur over certain time, across different groups of test takers in an EFL situation. The present study aims to analyse written performance of a number of English language learners over a year in a thick description to provide in-depth empirical data focusing on performance of test takers in terms of CAF. Previously, the majority of language learners' written performance was evaluated based on some scales without taking into account the qualitative performance from the SLA perspective. Therefore, the present study tries to bridge the gap between testing and SLA. As far as the first research question, which is the relative contributions of each of the features, complexity, accuracy and fluency is concerned, the researchers found a noticeable negative correlation between the complexity, accuracy and fluency of learner performance. Concerning the development of participants in writing skill as the second research question, students did not reach the benchmarks of Common European Framework of Reference (CEFR) levels. Moreover, it was observed that forms may not develop linearly among these three dimensions, and a learner's improvement in repeating a task does not guarantee that he/she will get the most from a target-language perspective unless it raises his/her awareness.