Project Based Learning? Or learning nothing

On a Wednesday during period two I teach a class a topic called Project Based Learning. I say the word "teach" very loosely as I am mainly there as an extra body in the room (alongside two other teachers) and to check the students literacy - that is whenever they produce a piece of written work I need to check it for spelling, grammar, punctuation and of course that it makes sense.

I say "check their work" in the most loosest of terms as well as so far this term I haven't seen any of it. Maybe it's because they don't know what to do. Maybe it's because they can't be bothered or maybe it's because the brief is so broad that they haven't got a clue where to start. 

But there's where Project Based Learning or PBL as it's commonly known in our school is different. The fact that the brief may be broad or the fact that little work may be produced throughout the course of the process doesn't really matter as the students are meant to learn by making mistakes in Year 10 so that they don't then repeat the same mistakes in Year 11.

What do you think of this way of learning?