I see, thanks for the reply
Do you have any idea if java 7 will be widely distributed in a couple of months or will it be a very slow process?
For schools, it will probably be at least another year, as lots of institutions upgrade their software during the summer holidays.
If you do chose to target 6, then I'd recommend developing on 6 too, instead of 7. Although you can set Java 7 to target Java 6, there is nothing to stop you accidentally using any new classes or methods which are exclusive to 7.