Task-based language teaching (TBLT) has occupied an important place in the field of language education; however, some of TBLT dimensions that pertain to the interaction between task design features, written corrective feedback (WCF), and learners' performance have not received adequate attention in past studies. To fill this gap, the current study investigates how task complexity, task condition, and their interaction determine language learners' gain from WCF. To conduct the study, 223 participants were randomly assigned into three experimental and one control groups. Participants in the experimental groups received a pretest, followed by three treatment sessions, during which they completed simple or complex writing tasks either individually or collaboratively. They received feedback on their performance and finally completed two posttests. Participants in the control group received pretest, posttest, and regular classroom instruction (instead of the treatment), but they did not receive WCF. Results of statistical analyses demonstrated that task implementation condition had a more highlighted role than task complexity in determining learners' gain from WCF, but the interplay between the two variables didn't affect participants' writing complexity and accuracy. These findings lend partial support to Skehan's Tradeoff Hypothesis and to Vygotsky's sociocultural theory of language development. Implications for language instructors and syllabus designers will be discussed.