I say really watch out for MH issues, especially if your child is quiet or shy.
My DD was shy, but made good friends even after moving primaries in year 5. She was popular there and happy.
Moved up to secondary and things slowly went downhill in year 7, felt v. anxious because the teachers were always angry (e.g. she did HW with around 20 questions, skipped one because she didn't understand, got all the rest right, and had to miss 2 full lunch times as a result).
There was stupid stuff like a whole English unit being 'about my dad'... This was a seemingly good school in a good area, so DD was one of few who didn't have much of a relationship with her dad.
Her friends made new friends, she just got lost on the crowd. Teachers didn't learn her name, nobody cared at all. By yr 9 everyone became v. grown up, started partying (and I assume drinking). School became too much for her.
Luckily she moved and things turned out okay-- but really keep an eye out, she became so unhappy so fast and I thought for much too long that she was just tired.