Your answer - middle school - I find it extremely young for this, which is extra interesting.
That year I sent an email to her teacher to let them know that I'm the one responsible for her not doing all the work and if that's a problem, we need to talk. It wasn't a problem.
The one class that was flipped was a relief because she could breeze through the lesson much faster than would normally be spent on it in class and the amount of time on exercises was limited to the class time slot.