Summer is a time of great potential for violin playing, and for progress. I know that the students who practiced and had lessons regularly over the summer last year made more progress and are further ahead than the students who took most of the summer away from violin.
There's also something to be said for a nice healthy break from your violin, but for the serious student wanting to make real progress, that break looks more like a long weekend, or a week at the most, rather than an entire summer.
For the serious high school student considering a major in music, a residential summer program can give them a taste of what that life would be like and let them see if it's what they really want to pursue in music.
Even for a student who just wants to progress in their high school orchestra, summer study is essential. In Northern Virginia, where I live and teach, the school orchestra are incredibly competitive. Just to keep up takes consistent and regular practice, and advancing takes tremendous effort and commitment.
I'm recommending to all of my students that they participate in some sort of summer program this year. It will give them a different experience than just private lessons (although I expect them to have some lessons with me in the summer months), and it opens them up to new ideas and perspectives. For the younger students, I'm recommending family Suzuki camps. There are wonderful Suzuki Institutes where students and families can have private and group lessons, parent sessions, and fun electives like music mind games or fiddle.
For my older students, I'm recommending a practice intensive camp. Especially for those who are in the process of rebuilding fundamental technique or those who want to move to another level quickly, I recommend summer programs which include some form of private study or have very low faculty-to-student ratio. Beware of cheaper programs that may be an orchestra camp with one conductor and 40-50 kids. It's a completely different experience, and I highly recommend the programs with some level of personalized instruction for the most progress.
If you're in the Northern Virginia area, here is the link to Violin Bootcamp, the program my colleagues at Potomac Arts Academy and I are designing. It's going to be a practice and technique intensive workshop, and the goal is for students to make a lot of progress in a short amount of time.