I live in Scotland so don't know how the English system works. I have seen loads of posts about school waiting lists and getting children in to schools. How exactly does this work, are schools not allocated by residential address?
Up here every address has a catchment school - the local school that your child is entitled to a place in, you can put in a placing request to have your child enrolled in one outwith your catchment, if that school has space once the catchment spaces are filled then your child gets a place, if more placing requests than spaces then there is a list of criteria to be met with some criteria having more weight than others.
Enrolment happens in January for the upcoming school year (starting in August) you cannot enrol your child before this.