Studying disagreement in STEM classrooms is one way to better understand students’ sense of belonging in a learning environment by linking the frequency of disagreement with how comfortable they are contributing their true opinions. I determined whether students’ frequency of expression of disagreement in an online STEM course is affected by group composition (gender, size, topic). Disagreement is measured in this study directly by quantifying how many students replied to prompted discussion questions with disagreement statements or when students ask and answer questions to clarify the disagreement. I predicted that students would express more disagreement when they were male, were in groups with less than four people, and discussed topics involving evolutionary processes and phylogeny based on conclusions from previous literature. The results showed that there was not a difference in disagreement rate across gender, there was more disagreement for "Population Genetics" and "Other Evolutionary Processes" compared to "Phylogenetics" and "Biodiversity," and there tended to be more disagreement for teams of five compared to smaller sized groups. These findings can be applied to future biology education research to improve the ways group activities are structured to be more inclusive of students of all backgrounds and to maximize true expression of opinions.