A challenge with flipped instruction is the pre-class preparation, where students independently learn fundamental content outside the classroom. For this pre-class learning, instructors typically assign videos with quizzes. However, this approach is the same for all and does not address differential needs. In a prior National Science Foundation (NSF) study with three schools, differences in the outcomes for blended versus flipped instruction in a numerical method course were not statistically significant, and the effect sizes were small. To diversify pre-class preparation and potentially improve outcomes in the flipped classroom, the instructor developed lessons using an adaptive platform via a new NSF grant. The adaptive platform provides personalized, flexible learning with multiple resources, including videos, text, quizzes, and simulations, with different paths depending on a student's progress. Adaptive lessons were implemented during two semesters in a flipped classroom, and the results were compared to (1) flipped instruction without adaptive lessons and (2) blended instruction. The comparisons consisted of direct assessments (i.e. exams) and student evaluations via survey. Analysis was done collectively for students and for several demographic groups. Based on direct and indirect measures, the flipped classroom with adaptive learning may be the preferred method for this and other STEM courses.