A friendly group is fine. The odd couple of mothers or threesomes who hang out more is also fine. But what is not nice is when there are several who have a kind of helping each other feel better than the rest thing going on. And yes, they do exist!!
I noticed the mothers in reception who were starting to network. They have coffee mornings. They have dinners. They have play dates. They vie for who is going to be class rep. When there's a school cake sale or some such, and even when their kids are way too young to make anything other than mud pies, they always always bustle in with a massive tower of perfect cup cakes on a special tiered thing from Lakeland with a really special carrying box for it all.
And they pass comment. They judge. They look at your clothes. They look at your kid. They look at your car. They ask where you live, what you do, what your 'husband' does. If they are married and you aren't, you may be admitted to the group as an occasional oddity and as a kind of disabled minority.
Etc.
OMG and woe betide if your kid is nicer/prettier/better at singing/dancing/gymnastics than theirs!
She definitely won't be invited round much in that case!
Next time we start at a new school, I'm going to say I'm married to a pilot or cardiologist (better still, paediatric cardiologist), and that I myself am a GP and trained psychologist but taking time out to be with the children. And that I've come in the little car but we have an Audi Q5 and a Porsche at home. And a house in France. And a designer dog.
Will see how it goes : )