This study examined how task type can affect the ways in which learners resolve lexical language-related episodes (LREs) and consequently how their vocabulary learning in the LREs is influenced. An intact class of Iranian learners (N = 24) of English as a foreign language were paired up to write a composition and complete a cloze task. The researchers recorded all collaborative dialogues and transcribed and analyzed them to detect lexical LREs. The LREs were divided into cognitive conflict episodes (CCEs) and non-CCEs on the basis of how they were resolved and engaged the learners. The results indicate a higher number of CCEs, entailing elaborate engagement, in the collaborative dialogues over the composition. The results also reveal that vocabulary gains were greater in composition. The authors suggest that language teachers develop tasks inducing higher cognitive conflicts.