Students' success in undergraduate STEM courses requires effective studying behavior, but also the motivation to enact it. Promoting students' achievement in STEM has commonly focused on either study strategies (cognitive) or motivational interventions; we hypothesized that combinations of these would be more effective. Using a Learning Management System for delivery, we iteratively developed and tested the effect of different combinations of one of four cognition-focused with one of three motivation-focused intervention modules. Participants were 3,092 undergraduate introductory biology students tested in 10 studies at 3 universities over 4 years. They were randomly assigned to either a no-treatment control condition or one of 17 conditions involving either single or combined intervention modules delivered over an entire semester. Course grades were provided by the instructor. We used meta-analytic techniques to capture the effect of students' access to the interventions on grades, and to test whether differences across experiments changed the effect size for the interventions. Averaging across the studies, the intervention had an effect of g = 0.30. All 10 moderators were significant: cognitive+motivational versus either one alone, timely access to the intervention, iterative development phase, type of cognitive or type of motivation module, the specific cognitive-motivation combination, university, academic year, semester, first versus second semester of biology, and course content. We conclude that combined interventions delivered via an LMS can meaningfully improve undergraduate students' course grades (corresponding to 6.6 percentage points on final course grade), with minimal extra work for instructors. However, these effects depended on a variety of contextual factors. [This paper will be published in "Technology, Mind, and Behavior."]