The flipped classroom is becoming a popular course structure in many academic disciplines, but particularly in STEM disciplines, including mathematics. Considerable research has addressed potential advantages and challenges of teaching a flipped course, as well as examining students' attitudes towards the flipped classroom. Studies on students' academic performance in a flipped classroom remain relatively scarce, and have shown mixed results. This paper reports on a study using a flipped classroom design, combined with interleaved practice, in a 5-credit precalculus course at a regional 4-year university. I evaluated the students' performance on the final exam compared to a similarly sized random sample of students from non-flipped sections of the same course. This evaluation was done by a single-blind student research assistant, to reduce researcher bias. I also tracked students success in the calculus sequence. Since grades in subsequent courses were determined by other instructors, they should also be free of researcher bias. I found the students in the flipped sections performed better on the final, with the difference being statistically significant. I found that the percentage of students completing subsequent calculus courses with a C--or better was not significantly different between the students coming from the flipped and the non-flipped sections of precalculus.