High School and Scouts/Drama

I haven't seen this in my game before. Usually when my child sims age up, they just stay enrolled in the same after school activity at the level that they were, and keep going to school as normal. I'm not sure because I havent heard of your situation to be honest, but I don't think the game really should be prompting you to quit high school, so I'm assuming it's probably some kind of bug or mods :/ It might be worth looking through your mods folder and seeing if you have anything that might be conflicting with school activities, or have something that gives kids the option to quit school (I don't think you can do this normally), so it might be a mod like that?

That does sound like either a bug or a mod conflict. I've previously had teen Sims do scouting and school at the same time without an issue, even a part time job along with that.

I'd say try disabling your mods and see if it's still a problem.