I would really encourage OP (and their child) to work on acclimating at the current school first. If you still want to transfer in December, you'll absolutely have time. But it's such an important experience for kids to go through a transition, maybe not have it go well at first, but stay positive and make a good faith effort. A lot can change in a few months. What feels like a poor fit might just be the natural adjustment process. If your child has social or academic concerns, they should talk to the advisor, the guidance counselor, etc. ASAP. Make use of all those resources that your tuition includes
That said, I think there are a few specific cases where deciding for sure to apply out now makes sense:
- the commute has turned out to be hellish or you need to move to a different area
- financial circumstances have made the tuition impossible and you need a way less expensive (or free) option
- you're unhappy with a large-scale, unchangeable component of the school, e.g.: secular v. religious, co-ed v. single sex
But anything less concrete than that is worth trying to work though. There's no guarantee a different school will be magically better!