Objectives: To create a system to enhance learning by encouraging students to think for themselves and express their ideas in classrooms. This study evaluates the effects of the new utterance reward system （URS） on student attitudes and achievement. Methods: Fourth–year medical students in the 2009 Hygiene and Public Health course were informed that they would get marks for each classroom utterance that expressed their ideas. We evaluated degree of classroom engagement in the course by comparing number of utterances before and after introduction of the URS in 2008 and 2009. To assess correlations between classroom engagement and student outcomes, we examined the relationship between number of utterances and exam scores. At the end of the course, we distributed questionnaires on student perceptions of the URS. Results: The number of utterances in 2009 increased compared with that in 2008. Students who made more utterances achieved significantly higher exam marks （epidemiology, r＝0.36, public health, r＝0.40）. Current grade point average rankings （CGAR）, used as an index of general competency, was a confounding factor in the relationship between the URS and achievement. We stratified students into two groups by median CGARs. Stratified analysis of the relationship between number of utterances and exam scores showed no association within the higher–CGAR group. However, this association was significant in the lower–CGAR group in the public health class （r＝0.31, p＝0.03）. Conclusions: The URS appeared to increase student participation in the classroom and positive perceptions on participation.