For everyone interested in computer science education: I just stumbled across the SIGCSE organization (ACM Special Interest Group on Computer Science Education) which organizes conferences around this topic.
The main (flagship) event is the annual SIGCSE Technical Symposium which is always located in the US (approx. 1500 visitors). Visit the sites of SIGCSE 2011 and SIGCSE 2012 to get a flavor of the programme.
For the rest of the world, the ITiCSE (Annual Conf. on Innovation and Technology in Computer Science Education) takes place at locations outside the US as well (e.g. ITiCSE 2011 in Darmstadt, Germany, in 2011). It attracts around 200 attendants.
Have a look at the SIGSCE 2012 blog to stay up-to-date on the next conference. By the way, Michael Kölling announced that there will be a Greenfoot event at SIGSCE next year.