I have to say, I'm not worried. In part, this is because my son's middle school seems awesome, with excited and engaged teachers. In part, it's because I remember my middle school years so fondly. It's an age when you're old enough to know what your interests are and how to pursue them--sometimes beyond what your parents can help you with--but you're young enough that your afternoons aren't so filled with homework and work and extracurriculars and your social life that you don't have time for yourself.
At this age, I spent whole days on nothing but me. I guess it wasn't until 9th grade that I started arranging music for whole marching bands--that's another story--but in middle school I painted, I wrote, and above all, I read. I would spend entire days reading. I would read books I liked over and over and over, which is why I am flattered but not particularly surprised when readers tell me they've read my books ten times (Endless Summer, usually). That kind of free time is luxurious and delicious and particular to being twelve.
As I am writing this, there was just a big BANG from my son's room. He was supposed to have gone to bed and NOT READ half an hour ago, but obviously he has dropped The Hunt for Red October, which he has hardly put down since I checked it out for him today, or something else has fallen off his bunk bed in his trek down the ladder to retrieve the forbidden tome. Whatevs. If his nocturnal reading habits remain what he gets in the most trouble for, middle school will be fun, and I'll take it.