When it comes to biology lessons in Germany, girls generally exhibit higher levels of self-determined motivation than boys. Previous research suggests that fostering student autonomy could be a way to effectively address this gender gap. To investigate gender-related effects in biology education, a sample of 303 sixth-grade students (M[subscript age] = 11.31 years, SD[subscript age] = 0.58 years) participated in a 3-h teaching unit on harvest mice that was taught in either an autonomy-supportive or controlling manner. The results revealed a significant effect of the treatment on self-determined motivation, with the effect being stronger for the boys. In the treatment with controlling teaching behavior, gender-related differences in self-determined motivation became apparent. In contrast, the gender gap was mainly smaller in the treatment with autonomy-supportive teaching behavior. Thus, the results suggest that satisfying the need for autonomy appears to be an effective means to help bridge the gender gap in biology lessons.