Examining task type effects on L2 writing complexity: understanding the moderating roles of goal orientation and flow

This study examined the impact of task type and learner-related variables – goal orientation and flow – on lexical and syntactic complexity in second language (L2) writing. One hundred upper-intermediate L2 learners in a university-level multilingual writing course completed four tasks (personal, narrative, expository, and argumentative) over four weeks, alongside goal orientation and flow questionnaires. Essays were analyzed using fine-grained lexical and syntactic metrics, and effects were tested using linear mixed-effects models. Task type significantly influenced most complexity measures, with argumentative and expository tasks generally eliciting more sophisticated structures than narrative and personal tasks. Mastery and approach goals predicted greater lexical diversity and lower-frequency vocabulary, while avoidance goals showed mixed patterns. Flow dimensions – especially clear goals, task relevance, challenge – skill balance, and autotelic experience – moderated task effects mainly at the lexical level, enhancing diversity, sophistication, and semantic variation in context-dependent ways. The findings highlight the interplay between task demands and learner engagement, suggesting that genre scaffolding, explicit goal-setting, and cognitively challenging yet personally relevant tasks can support advanced L2 writing development.