Students could benefit from working in an environment such as the phpBB environment as it, if used correctly, would encourage them to work together. It could also be used to see other peoples views on certain topics ("what do you think of character x in this?"), and for feedback on stuff like projects. They could also ask each other questions etc.
The obvious way to get students to work with phpBB is to set a board on, say, the school website or something, and to have them a lesson each where they are encouraged to sign up and take a look about. It would also help (probably) if you had a few older students (or maybe teachers?) who were prepared to spend quite a bit of time on the board to begin with, to make students feel as if they could ask questions and could be reasonably certain of getting an answer. Over time, the need for these students would decrease. Students should not be forced to use the website - this would just drive them away.
You would have to consider any advantages compared to what they use currently - Facebook and Wikipedia. As someone doing A-levels at the moment, I'm reasonably confident that if I ask a question on Facebook, it will be answered in a minute or so - that is something that you would never be able to achieve with a bulletin board. With Wikipedia, I can find answers to my questions in great detail very quickly. The advantages I can think of over Facebook is that answers would probably be better quality (I get some very vague answers sometimes), and questions that people have asked before would be visible and searchable - and chances are, if someone has had a question one year, someone else will have it the next. I can't think of many advantages over Wikipedia, short of that Wikipedia often goes into too much detail and can be confusing, while a student having something explained to them by their peers will usually have it explained to them at their level.
Just my 2¢ (probably just late night ramblings and not very useful, though)
—Douglas CrockfordView my MOD, phpBB Mobile