Delivering an inadequate amount of light to a light-cured resin will result in a resin that is inadequately cured. This study measured the radiant exposure that students delivered to a simulated restoration to determine if instruction with immediate feedback increased the amount of light they delivered. The amount of light (radiant exposure in J/cm(2)) delivered to a simulated restoration by sixty-three dental students using the same curing light for twenty seconds was recorded. The experiment was repeated after the students had been given detailed light-curing instructions together with immediate feedback using the MARCPS system. Initially, the students delivered between 1.4 and 17.5 J/cm(2) (mean±SD: 9.8±3.5 J/cm(2)). After receiving instructions and feedback on their light-curing technique, they delivered between 6.7 J/cm(2) and 17.8 J/cm(2) (mean±SD: 13.2±3.3 J/cm(2)). ANOVA and Fisher's post hoc multiple comparison tests showed that providing immediate feedback on the students' light-curing technique made a significant improvement in the radiant exposure they delivered (p<0.05). It was concluded that many dental students in this study were not using the curing light properly. After the students had received one session of additional instruction and immediate feedback using the MARC-PS, they delivered 35 percent more light energy to the same simulated restoration. Students who were closer to graduation showed a greater improvement in their light-curing technique (p=0.0091).