I'll caveat this with I am very stressed in general and have my own complex history with social anxiety and bullying.
My dd is 7, in a small-ish school and has been there since reception. I've noticed the last year or so the dynamics are getting uncomfortable (and the cliquey mum groups don't help). My dd always seems to be the one left out, her teacher says she appears to have friends and doesn't seem to struggle/always plays with someone or a group at play times but she's never invited to parties or play dates while I see most of the others do.
One of the mums, a bit of ring leader in the cliques has been fucking awful, I've been friendly with her since the dd were babies in nursery together but hers recently got into football and is obviously no one else could possibly be as talented as her dc (who are twins and this plus football is their entire identity and they are treat like some kind of messiah because they happen to be twins)... a few things have wound me up this last week like her saying 'oh you're so lucky your dd isn't as fit or good at everything like mine!' And 'your weekends must be great because dd doesn't get invited to these parties you are so lucky she isn't popular like mine!'. She's a 7 year old kid ffs, take shots at me fine but why her? This has been getting progressively worse over the last year or so and I suspect things have been said to other parents.
Most other parents ignore me completely, most grew up here and know each other while I moved just before dd was born and no roots locally plus I work ft which isn't common at this school.
Tonight I saw photos from the school about a draw (names in a hat) they did where x number of dc won a day out. Wouldn't you know the twins won... they win every single competition and every time they'll run up to my dd 'we won and you didn't! Haha' type of thing and the mum almost joins in 'you couldn't do it anyway could you? You can't run ad fast as/do this as well as the twins' (again, this is an adult talking to a 7 year old!). I know the school don't do these things fairly but I feel like they could at least try to hide it!
My dd is a lovely little girl, a bit quiet so not often recognised in class because she just gets on. Which is fine, that's her and she's doing well, has lots of interests of her own and knows her own mind (also can't be arsed with any drama so just walks off when bickering starts). I think she might do better with a fresh start in a new school, but dh thinks I'm overreacting and has had a strop at me when I brought it up.
I know my own issues may cloud my thinking, but conscious bias isn't necessarily a bad thing.