This study examined the extent to which textual enhancement incorporated into the post-task stage of task-based reading lessons can promote development in second language (L2) grammatical knowledge. The participants were 49 child language learners who participated in task-based reading lessons in their own classroom contexts. They were randomly assigned to two groups, one being exposed to textual enhancement and the other not. The experiment adopted a multiple-exposure design involving six treatment sessions over three weeks. The target construction was the third person singular -s morpheme. Pretest-posttest development was assessed with a grammaticality judgement test. The results revealed a small but positive effect for textual enhancement. We attributed the relative success of textual enhancement to a combination of factors: use of a multiple-exposure design, the incorporation of textual enhancement into the post-task rather than the during-task stage, age of participants, and prior knowledge.