MCPS has a honors chorus that has try-outs for piano accompaniment, but that's not really at the school.
My child has also played piano since 1st grade, but she started with violin also in 4th grade. Since she reads music and knows about tempo, etc., already, it's a lot easier. She practices piano a lot more than violin. We consider piano her primary instrument and the violin is just for the benefit of playing with a group, but if she ends up liking violin more that could change.