The goal of the study was to improve high school students' problem solving performance as they worked with IMMEX, an online chemistry problem solving simulation. The intervention included brief text messages added to the simulation to encourage students to reflect on their problem solving strategies and to adopt more effective problem solving behaviors. Students who worked with the message-enhanced version were more likely to solve the problems correctly, and to use more effective problem solving strategies than students who worked with the original version. Benefits of the messages were observed for students with relatively poor problem solving skills, and for students who used exhaustive strategies.