I can see it from both sides ... before my dd went to vocational school, summer schools, nyb etc were a great opportunity to meet like minded individuals, make new friends, get seen and gain access to fantastic facilities and different teachers ... it's amazing what they can pick up in a week that will stay with them.
Now that dd is at vocational school all of the above still applies, but as JulieW says, two months off is a long time without any dancing and whilst it is important for growing bodies to get plenty of rest over the holidays to prevent future injury, once my dd has re-charged her batteries she starts going stir crazy over the summer if she can't dance!
dd usually finds that there is a good mix/balance of vocational and non-vocational students at summer schools.