One of the persistent challenges in science, technology, engineering, and math (STEM) education is increasing interest, learning, and retention, particularly with regard to girls and students in underserved areas. Educational curricula that promote process and content knowledge development as well as interest and engagement in STEM are critical in supporting student success and pathways to careers in STEM-related fields. One new and innovative method for promoting STEM learning is animal-based curricula, which can provide the opportunity to introduce students to science and engineering principles in an active, engaging way that promotes an optimal learning environment. The goal of this study was to pilot test the effectiveness of animal-based curricula in motivating middle-school students' interest in science and engineering, as a gateway to them learning more broadly about science and engineering careers. The present study used data from two veterinary medicine-based out-of-school time STEM programs for middle school students. Students in both programs reported a significant increase in scores on interest in engineering after completing the program, but no significant difference in science interest scores. The findings from these pilot data provide exploratory information about the potential effectiveness of animal-based STEM education as a strategy for increasing interest in STEM careers for middle school students.