Join.me is another quick web conferencing option. The FAQ claims a meeting could support up to 250 connections. That's more than most free options. No webcam or voip audio - instead, it's all about screenshare and conference calls (long distance charges may apply). The presenter can also share screen control with any viewer - making hands on tech support a possibility.
Could be handy when you need to see what your student sees. Or perhaps for some live assessment of computer skills.
In case you missed it, here's a link to our Web Conferencing episode.