Self-beliefs are important determinants of student choice and success (Wigfield & Eccles, 2000) and are informed by student educational experiences, such as prior success with a task (Bandura, 1986). The potential for Computer-Based Interventions as self-belief-supporting learning environments is examined in this study, focusing on the mathematics software, Spatial Temporal (ST) Math. ST Math includes elements theorized to support student self-beliefs, including informative feedback and a self-pacing structure. Using a randomized control trial, we find that students who play ST Math have higher mathematics self-beliefs than their control counterparts, and that ST Math operates through self-beliefs to positively influence achievement. ST Math's impact on student self-beliefs is strongest for those students who had lower mathematics achievement scores.