So in the school where I work (very middle-class state primary school in an affluent part of North London) each class has to do two assemblies a year. But unlike most schools, where assemblies are low-key affairs and consist of the children mumbling something about what they've been studying in class, assemblies in my school are a BIG deal (all parents and grandparents attending), and you're seen as something of a failure if you don't put on a full-scale Chekhov production in the original Russian. I'm as much to blame for this as anyone, as I put in far too much work and energy into my assemblies, thus ensuring that the rest of the staff feel they have put on something equally ambitious..
Anyway the topic I chose for this assembly (and it really is the teacher's choice - you can do anything you want. It's basically your opportunity as a class teacher to present your creative vision to the school!) was the internet. And it was sick.