Scientific practices are the skills used to develop scientific knowledge and are essential for careers in science. Despite calls from education and government agencies to cultivate scientific practices, there remains little evidence of how often students are asked to apply them in undergraduate courses. We analyzed exams from biology courses at 100 institutions across the United States and found that only 7% of exam questions addressed a scientific practice and that 32% of biology exams did not test any scientific practices. The low occurrence of scientific practices on exams signals that undergraduate courses may not be integrating foundational scientific skills throughout their curriculum in the manner envisioned by recent national frameworks. Although there were few scientific practices overall, their close association with higher-order cognitive skills suggests that scientific practices represent a primary means to help students develop critical thinking skills and highlights the importance of incorporating a greater degree of scientific practices into undergraduate lecture courses and exams.