Do students from small high schools show fewer understandings and more misconceptions of biology concepts than students attending large high schools? Fifty students attending large high schools (enrollments exceeding 900 students) and fifty students attending small high schools (enrollments less than 150 students) were randomly selected and than evaluated on their understandings and misunderstandings of four biology concepts: diffusion, homeostasis, food production in plants, and classification of animals and plants. Students attending small high schools showed less instances of understanding and more instances of misunderstanding the concepts of diffusion and homeostasis. These differences could be related to a higher percentage of students in large schools capable of formal operations; sound understanding of diffusion and homeostasis required students to use formal operations. No difference was observed between the large and small school samples for the concepts of food production in plants and classification of plants and animals. Students in the small school sample lived in agricultural communities and their daily experiences allowed them to develop some understanding of food production in plants and prevented instances of misunderstandings from being developed. Classification of animals and plants required concrete operations to understand; therefore, students in small schools were capable of developing sound understanding as well as students from large schools.