To tell the truth, I love assembly days.
With my school, they tell me I can either stay in the lounge or go outside an observe. Honestly, if given the chance to enjoy the sunshine, I'm gonna take it.
A bit much to be shooed away, but I'd suggest asking to come. Someone mentioned it, but these assemblies are a social experience for the teachers as well as students.
For example, on sports days, there's very little required of teachers aside from writing down results. The entire day, we're outside drinking beverages and eating fruit. Yeah, I don't know every tidbit of conversation, but face-time is important. Show you're willing to spend time with them regardless of languag ability and they'll appreciate it.