BioEYES, a nonprofit outreach program using zebrafish to excite and educate K–12 students about science and how to think and act like scientists, has been integrated into hundreds of under-resourced schools since 2002. During the week-long experiments, students raise zebrafish embryos to learn principles of development and genetics. We have analyzed 19,463 participating students’ pre- and post-tests within the program to examine their learning growth and attitude changes towards science. We found that at all grade levels, BioEYES effectively increased students’ content knowledge and produced