DCL operates by age, not school grade. My DD has been in each kid venue--club, lab, and now the Stack based on age. She chose to celebrate her 13th birthday in The Stack.
Ok, she's been a relatively sheltered kid in some ways, and is very mature in other ways. She was educated at home until this year except for the classes she takes at a local university. Thus, she has been in a class setting with 18-20 year olds, but her only "same age" experience was at church--frankly, she finds most kids her age to be rather superficial.
Both of our cruises (13th birthday and one since) have been great. There is always a counsellor in The Stack--she says they are "teen aged wanna-bes." There are relatively few scheduled activities, but there is a long list of things the kids can do--just ask the counsellor for supplies. She loves the Stack, and spends most of her time there. In fairness, our cruises were during the school year, so there were relatively few teens on the ship. The kids are broken into age groups like the younger kids are.
So...basic question...where is a 7th grader? It depends on age. Would I place an early 13 year old in the Stack? Absolutely. Think about it. Would your new 13 really want to be in the 10-12 year old group??????
On our second cruise after she became 13 (she was 13 years, 6 months), there was a small problem with a certain young man who didn't want to take "no" for an answer. It was very promptly handled by the staff. DD was given a "code" to give the counsellor if she had any more problems with him. He was talked to and told that he wouldn't be allowed to return if he bothered her again or if he retaliated in any way.