You were kind enough to admit you're experience is with college students. But mine is with high school kids and let me convey one simple conclusion I've come to after ten years of wrestling with this stuff.
Discovery definitely has its a place (and it's a pretty good sized one), but in and of itself it doesn't significantly improve student outcomes. There are two things which impact student performance significantly. One is intelligence which generally can't be taught. The other is study, pure and simple. Kids who apply themselves succeed; those who don't won't. I wonder how many of us would expect our own kids to go through school without study. Not very many, I think.
The radical reformers have trouble distinquishing curriculum and motivation. In my mind the correlation between the two is pretty small, enough perhaps to produce marginal improvement, but not more.