In this study, we examined how high-school students utilized a hypermedia learning environment (HLE) to acquire declarative knowledge of a historical topic, as well as historical thinking skills. In particular, we were interested in whether self-regulated learning (SRL; Winne & Hadwin, 1998; Zimmerman, 2000) processing was related to the acquisition of declarative knowledge and historical thinking. We found that, using the HLE, participants did learn from pretest to posttest, and that they most often engaged in strategy use SRL processes. However, the frequency of participant use of planning SRL processes, not strategy use, was predictive of learning. This study has implications for how educators use HLEs to foster historical thinking skills, and suggests that scaffolding planning skills may facilitate students' use of computers as cognitive and metacognitive tools for learning (Azevedo, 2005; Lajoie, 2000). (Contains 4 tables.)