I’m an old timer who hasn’t posted here in a while. My kid has both bachelors and masters degrees in music performance.
Summers…
After 8th, 9th, 10th grade went to New England Music Camp
After 11th and 12th grades went to BUTI
After freshman and sophomore year of college went to Eastern Music Festival
After junior year of college did a trumpet workshop at Northwestern and played in an orchestra for three summer shows on cape cod. He was a substitute fo this ensemble but was called.
After senior year of college went to Aspen
After first year of grad school, played in a school ensemble in the summer at a summer music thing they sponsored.
After second year of grad school…and graduation…started a job touring with a brass ensemble.
In all cases, he took instrument lessons all summer long, either privately or as part of his summer program.
@Compojazzm, S was so happy to be free from the time sink of high school, and with the prospect of August band placement auditions ahead of him, that he spent that post-high-school summer practicing and transcribing more than before. Then same with winter break. And pretty much the same this summer.
My kid took piano lessons the summer before freshman year in hopes of testing out of the piano requirement, in addition to lessons on her primary instrument. Summers during college, she has been playing in two local community bands, working, and taking lessons on her secondary instrument (for fun). And lots of practicing.
This is such a helpful thread - thanks to everybody who is responding! We are getting a much better idea of what the future will look like.
Be sure to look at summer program faculty lists. Great way to meet faculty from schools your child may want to study with for college/grad school.
Summers:
Rising HS freshman Conservatorio PR Musical Theater Summer Program
Rising HS sophomore Interlochen Voice Program
Rising HS junior Interlochen Voice Program
Rising HS senior Oberlin Vocal Academy
Rising college freshman Conservatorio PR “Campamento Canto Lirico” Summer Program
Rising sophomore home resting
@coloraturadad - resting and recharging are good for the soul and the voice! 
I bet you are loving having your student home for the summer.
My daughter, a rising college junior, is working about 20 hours a week at a job that doesn’t strain her voice, singing weddings and funerals, resting and seeing friends, and preparing for a 2-week program in August. If the program is good I’ll report back! She’s been able to continue lessons with her teacher over the summer which has been really nice.