To add to Jason's point, I think FIRST adds a lot to the intangible skill set of future engineers and scientists. FIRST gives you opportunities to make budgets, presentations, and persuade people of your opinion long in advance of your peers.
FIRST's successes won't be measured in terms of % on tomorrow's test, it will be measured by the leaps and bounds of progress wrought by FIRST's alumni.
It's no scientific study, but I've found a pretty impressive correlation in my own college experiences between competent people you can trust to get things done and kids who did FIRST.
Best of luck getting the actual data you need!
