I'm a IT/Computing teacher in the UK. We've only just started to teach Computer Science recently and although I was a developer before retraining as a teacher I chose Visual Basic.
Why? Well, we don't have to pay to install it, our technicians are happy to install it, the GUI design stuff is easy for students to use, I think it is easy to learn quickly and most importantly it allows our students to get high marks easily. Also I'm the only person in my school who can program - others will have to pick it up as the number of classes increases - again VB is easy for a novice to learn.
The exam board dictates what programing assessment is to be done and the amount of time it is to be done in. As much as I'd be happy to teach another language VB is the best fit in this case.