Argumentation can contribute significantly to content area learning. Recent research has raised questions about the effects of discussion (deliberation) goals versus persuasion (disputation) goals on reasoning and learning. This is the first study to compare the effects of these writing goals on individual writing to learn. Grade 7 and 8 students learned about buoyancy through argument writing. A 2 x 2 x 2 between-subjects pretest-post-test randomized experiment was used to investigate the effects of two types of argument writing goals (persuasion versus discussion), two distributions of writing sub-goals (segmented versus clustered), and two levels of writing achievement (low versus high) on bias/balance in reasoning, cognitive load, and learning. Results showed that segmented sub-goals were rated less difficult than clustered sub-goals. In a three-way interaction, for high-achieving writers, sub-goal segmentation reduced cognitive load in discussion writing, but increased it in persuasive writing. Argument goal type and sub-goal distribution affected bias/balance in claims and inferences. These results suggest that the effects of argument goal type are moderated by sub-goal distribution and previous writing achievement.