My teens go to school every day, sit in class, do their homework and have good reports for their exams. The bar for performance is also maxed out and the check mark is there yet their grades are not going up and they are stuck at C Student
Unclear but grades just seem stuck as long as you go to school with your Sim.
It does work to get better grades if you send your Sim to school alone.
Because of this, the solution is to go to school with your Sim until they are almost maxed out or maxed out.
Make sure the teens do their homework and then send the teen to school on their own. If this doesn’t work, try again. Make sure their performance bar is still close to maxed and hasn’t fallen down. If it did fall, you can just go with them to school again until they are back up.
There are also no school projects from parenthood if you go to school with them. Afaik you get them on Monday so Monday seems like a good day to send them alone if you also want a project.