Learners' choices as to whether and how to use visual representations during learning are an important yet understudied aspect of self-regulated learning. To gain insight, we developed a "choice-based" intelligent tutor in which students can choose whether and when to use diagrams to aid their problem solving in algebra. In an exploratory classroom study with 26 students, we investigated how learners choose diagrams and how their choice behaviors relate to learning outcomes. Students who "proactively" chose to use diagrams achieved higher learning outcomes than those who "reactively" used diagrams when they made incorrect attempts. This study contributes to understanding of self-regulated use of visual representations during problem solving. [This paper was published in: "ICLS2022 Proceedings," International Society of the Learning Sciences, 2022, pp. 1649-52.]