Today I tried a new approach. Using join.me rather than the projector in the room, I had the class view my screen. Some were a little freaked out that stuff was happening on their screen without doing anything themselves. But most of the girls immediately discovered the chat feature.
Now they could only chat with each other in the room, and I could see all their chatting, but that was not the point of the screen share. I really wanted them to see what I was talking about.
So first impressions: great tool that I could use often. I just wish I could turn off the chat feature. FYI, after I discontinued the session, the girls were still able to chat with each other until they closed their window.