Where are Your Students in SL?

I'm sure this discussion is happening all over the edu-web, but I just joined this group and it seems like a good place to get some ideas. I love the idea of having a class (or classes) interact in SL, but obviously main grid poses problems, and teen grid seems to me to be a hassle because (a) you need to purchase your own island (right?) which seems very pricey, and (b) are teens really going to be interested in utilizing that space, or are they just going to go home and log on to the main grid?

Love to hear your thoughts on the matter