It isn't really much to do with the parents I'm afraid. The school has it covered and will normally inform parents by letter a couple of weeks before the teacher leaves although the teacher may mention it earlier.
We were told in February that our reception teacher would be leaving next week. I think most parents knew 2-3 weeks before the official announcement though, as her job was advertised in the local paper.
I would say a week max is normal too. They like to have everything in place, and it doesn't help anyone to know 4 weeks early. we had a letter home yesterday about a teacher leaving at the end of term. it gives 4 days to say good bye but stops over anxious parents spendin g loads of time getting worked up. Children are used to having other teachers, eg for non-contact time, training, sickness, so tghey should adapt quite quickly and in a good school there will be a handover from one teacher to the next.
I think a week or so is normal. The school clearly knew a while ago as they had time to appoint someone else. If you tell children and parents too early it can cause hysteria! Some parents start stressing and want to see head to discuss how it will effect little jimmy and wanting to know who is taking over. Children get upset and worried. Much better to wait until last week and then introduce new teacher as you do it so no uncertainty or stress! It us normal to give a few days so parents can go cards or presents if they wish.
We were told today that DD's teacher is leaving on Wednesday (end of term). As it happens we already knew, as the new teacher went in to meet the children yesterday and DD told us about her.
But my question is about how much notice is it normal to give parents of a change of teachers - assuming it's something like a resignation and nothing unexpected? Is it a case of waiting until the new teacher has met the class so the kids all find out together?