As a student who graduated early from high school I would say it all depends on your kid. There is a huge disconnect from high school if you aren't in the grind of it every single day interacting with people, and although I went right into a junior college and took a full load of classes that counted towards my degree while working I never was able to get that connection back with my friends I used to see every single day. The main thing that I missed overall was the routine of being in school, taking tests, studying, writing everyday, ect. However, I would never do what I did differently. I was done with that chapter and was mentally ready to move on. I would say if your high schooler is doing it for the right reasons and doesn't want to waste their time, then it sounds like a great idea!