[trigger warning]
From BBC News, the results of an NSPCC and Lottery-funded report on violence in teenage relationships. 90% of teenagers (13 to 17) have been in an intimate relationship. Of those:
One in six [girls] said they had been pressured into sexual intercourse and 1 in 16 said they had been raped. Others had been pressured or forced to kiss or sexually touch.
A quarter of girls had suffered physical violence such as being slapped, punched, or beaten by their boyfriends.
[...]
Girls also reported that they suffered more repeatedly in relationships and at a younger age.
[...]
Unlike most boys, girls often felt they had little choice but to put up with the abuse because they felt scared, guilty, or feared they would lose their boyfriend.
It's not, perhaps, surprising that violence in relationships starts so young, and occurs in teens as much as it does in adults. This, though, is apparently the first detailed study of it, which did surprise me. I wonder if any follow-up studies on younger children are planned.
It makes it very obvious that people need teaching very early - before 90% of them have already been in a relationship - what a healthy relationship looks like and what an abusive relationship looks like. Expecting them to learn by example just doesn't work.
(It's not clear from the NSPCC press release whether the report considered same-sex relationships, since all the examples they give are heterosexual, and I can't find the report itself on their website)
Edited to add: A comment at the F-Word article gives the report. Currently only the executive summary is available. It's worth reading (and yes, they did cover same-sex relationships)