We introduce a choice-based assessment strategy that measures students' choices to seek constructive feedback and to revise their work. We present the feedback system of a game we designed to assess whether students choose positive or negative feedback and choose to revise their posters in the context of a poster design task, where they learn graphic design principles from feedback. We then describe an empirical study that sampled one hundred and six students from a US middle school to evaluate the feedback system. We make the following contributions: (1) describe the design and implementation of a novel feedback system embedded in an assessment game, Posterlet, (2) outline an approach to analyze graphic design principles automatically to provide contextual feedback in a novel poster design domain, (3) show that choices to seek negative feedback and to revise correlate with in-game performance, and most importantly, (4) show that choices correlate with in-school achievement: the choice to revise correlated with both in-school performance measures (Science and Mathematics grades), while the choice to seek negative feedback correlated with students' prior standardized scores in Mathematics.