As you said get involved. Also get the student comfortable self advocating. Public HS are a lot bigger than private. If there is a problem, question, concern, or information you want, the student needs to be willing to seek out the teacher, counselor, or assistance needed. Often times the help is there, but most times no one is going to seek you out. Be prepared to switch from a big fish in a small pond to a small fish/medium fish in a large pond.

Thanks PPs

No specific advice, just sharing that I went to an MCPS high school after doing private for K-8 and by the end of freshman year my friend group could not even remember that I didn't go to middle school with them.

Might help to know what HS.

I don't know about the transition from private, but the best thing my kids did when transitioning from MS was to get involved in the clubs in their HS. I think the same advice would apply to your DC.

Any tips to make transition easier for a new student at an MCPS Highschool? Other than clubs / trying for sports? Any other tips? If you child joined MCPS in Highschool, appreciate any tips, and what has helped your teen with the transition.