When my dc's started school I didn't know anyone and had been pre warned about the cliques and bitchiness......tbh though it's no different to the office in reality.
I smiled, I chatted and I have got to know some of the others and made some great friends. Sometimes I chat until 11 (what a crime!), sometimes I help out at school, sometimes I have no time to chat and am dashing off somewhere.
I smile and say hello to everyone I pass on the way in/out - some say it back, some blank me (perhaps they don't hear), some will engage in a longer chat......I don't lose sleep over it though!
A group of us get on especially well - our dc's are friends and we meet up with and without them. Are we seen as a clique? I hope not, we don't exclude people, we are just a group of Mums with things in common.
When I was at work there were gossips, bitchy people, stand offish people, nice people, busy people, chatty people, quiet people, people I liked, people I avoided like the plague........in the playground it's the same.
Imo it's easy to moan and bitch - you get out what you put in.
SG