I'm playing Twinbrook. The Stary Community School is still there, and I've added the Par Excellence Preparatory School premade community lot to a 40x40 lot. The only action my kids have for Par Excellence is "Attend Painting Class", Visitors Allowed or not. What am I doing wrong?

They are already enrolled in a school. Students will not automagically change schools. You could bulldoze the Stary school which would give you the opportunity to enroll them in the new school, then re-place the Stary school. New children who enter the game will enroll in the school closest to their home. Also there are some mods that allow you to control the schools. Check the mod section here on MTS, and I think there are some functions in Twallan's suite that may also help you. I don't know if Awesomemod offers anything that would help.

To add to this, from what I've seen it appears to be 'as the crow flies' and not closest by route- leading to some interesting school bus routes if your town is divided by a river!

If you want to transfer kids to a different school, you will want AwesomeMod for that feature. Otherwise there is no normal in-game way to change schools.

You could use [MasterController]'s "Choose School" interaction to move the sims if you wanted.

It was updated a while ago to differentiate between rabbitholes during the selection process.

Thanks for the help everyone! The neighbourhood kids are going to the correct schools and congestion has been alleviated.