I lived in Dorset as a young child - my parents are now in Somerset, and moved when I was a young teen. I was at boarding school during term time but the holidays could be loooong!
Unless you ride or are into country pursuits, as a teen in a very rural place, it can be boring! I did ride, and was very lucky that we had friends with swimming pools, tennis courts or sailing boats, so we had fun things to do - but we still had to rely on parental taxis until we'd passed our driving test, as public transport was (and still is) almost non existent. That brings a whole other level of worry (teens, cars and alcohol!) which I now appreciate as my own children are late teens now.
I adore visiting my parents, as do my children, but we mostly spend time at their house and in their large garden - going out to do anything involves a drive, and in the summer, getting out and about, or to and from the West Country is a total pain in the neck. Given that Labour, in their infinite wisdom, have decided that there won't be any road improvements to the A303 any time soon, it will only get worse!
If you are going to move, I'd probably choose to be close to Dorchester or Bournemouth - one of the larger centres, where there are good schools, but also a bit more for teens to do, and away from the summer gridlock of Bridport, Swanage etc.