Problem based learning

I like the idea of problem based learning however the amount of time dedicated towards implementing projects is in my opinion a bit much. The results from the article appear impressive but are they only reflected on their IGAP scores? Perhaps I don't have enough experience with problem based learning projects in my classroom but even with direct instruction and limited (5min or so) group collaboration I still feel like I cant give them everything I want in a lesson. For me the big concepts and the connections socially, economically, and politically are what I try to accomplish. I feel I would severely short change my students if they didn't understand history and why things happened the way they did. Can problem based learning solve this for me? I also worry that at least in this article the students are simply studying for the test and we are once again catering to funding and not academia. I just wonder how much they miss by doing this, its like post-holing for futures in cubicles.