Large class sizes appear to have the largest negative impact on females in STEM subjects, according to a new study by Cornell researchers.

In an analysis of data from 44 institutions around the world, including Cornell, 5,300 interactions between students and their instructors were recorded over two years. It was found that class size began to negatively impact student performance when there were more than 120 students enrolled in a lecture.

“We show that class size has the largest impact on female participation, with smaller classes leading to more equitable participation,” Cissy Ballen, a former postdoctoral researcher in the Department of Ecology and Evolutionary Biology and now an assistant professor at Auburn University, said in a statement.

“We also found that women are most likely to participate after small-group discussions when instructors use diverse teaching strategies.”

Past research has shown that large class size can be challenging for certain demographics, including first-generation students and underrepresented minorities.

“What we show here is that the deficit is not with those students, but rather with the classroom,” study co-author Kelly Zamudio, the Goldwin Smith Professor of Ecology and Evolutionary Biology in the College of Arts and Sciences, says in a statement.

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“If you want participation by everyone, then the classroom has to be an equal, open arena for everyone.”

Zamuido added that to achieve diversity in STEM, mentors will need to pay attention to the classroom climate.

The study, “Smaller Classes Promote Equitable Student Participation in STEM,” was published July 24 in Bioscience.