This study examined the effects of an intervention that engages student voice in classroom assessment on student perceptions of power, motivation, and attitudes towards assessment in a STEM context. The intervention and survey followed first-year students enrolled in a year-long STEM course (n=240). Half of all sections were randomly assigned to the intervention; here, TAs solicited student voice in participation grading criteria. Linear mixed models were used to analyze effects of the intervention. While the intervention did not result in main effects for outcomes of interest, longitudinal changes in perceptions of power, motivation orientation, and grades were found for all students from Fall to Spring. The intervention did, however, have promising impact on motivation and power for first-generation students and those whose TA changed from Fall to Winter, respectively. Implications for students in STEM, particularly those from marginalized backgrounds, and future directions for research and practice are also discussed.