hello, thought I would share my story and hope it helps.
My DD1 joined a school when her primary closed (amalgamated with others), we managed to get her a place in a lovely Catholic school and she was very happy.
Applied for DD2 to be given a place, head actually told me not to bother adding other schools, not a problem, blah blah.
Day of finding out - she had no place and was offered a school which was not good (the new amalgamated school) terrible offsted etc.
I cried, got angry, found out that DD2 was 2nd on the waiting list.
Should just mention my DD1 has had emotional issues due to previously moving schools, and was happy and settled at this school, felt we were making progress.
They didn't care - class was full, not practical to have 2 children in 2 schools I just couldn't see how this could be done.
So I didn't appeal, I had no grounds other than my life was being made difficult, 10 familes did appeal ICSize, all failed.
I decided to apply to the next authority to us, (we live in between 2), went to see a school, loved it, broke news to DD 1 that she needed to move, caused problems and I won't lie, it was terrible for our family.
Learnt to drive to be able to get them to new school in 5 months, bought a second hand car. Failed first time, passed day before they started in Sept 2008.
Now, things are more settled, the girls have adaped. It was difficult for DD1 and 2 to make friends, DD1 hda been thru this before DD2 joined Reception and all the other children had done a year together at nursery.
I just want to say, it's not the end of the world, you can come up with something else, I had to change my childminder of 6 years, only to find someone just as wondrful, I had to change my hours at work, everything...all because of one decision.
At the end of the day if you can prove that they applied the admission criteria incorrectly, go for it and appeal, if not, the fact of the matter is, the changes to your life do not mean much to them, if the class is full, it is full.
Sorry if any typos I have false nails on and it's difficult to type !
ALL THE BESTx