For years, skeptics of project-based learning raised a fair objection: the studies were small, the schools self-selected, the evidence suggestive rather than causal. A randomized controlled trial conducted by researchers at the University of Southern California, funded by Lucas Education Research, answered it directly.
The design
Researchers randomly assigned teachers of AP U.S. Government and AP Environmental Science — across five predominantly urban districts — to either a project-based curriculum (Knowledge in Action) or their usual instruction. Because assignment was random, differences in outcomes can be attributed to the teaching approach itself.
The results
- Students in the project-based courses earned credit-qualifying AP scores at a rate 8 percentage points higher than the control group in the first year.
- After teachers had two years of experience with the curriculum, the advantage grew to roughly 10 percentage points.
- The benefits held for students from low-income households, who were a larger share of the sample than is typical for AP test-takers.
The most striking detail isn't the size of the effect — it's where it showed up: on the College Board's own exam, the most conventional measure of achievement there is.
Why it matters
The finding dismantles the supposed trade-off between engagement and rigor. Students weren't doing projects instead of mastering content; the projects were how they mastered it. Inquiry isn't a detour around achievement — done well, it's the shortest path to it.
It also matters that teacher experience compounded the effect. Inquiry teaching is a skill that grows with practice and support — which is exactly why infrastructure for designing and refining units, not one-off lesson ideas, is what moves schools.
