Legally, every child must be in school in the term following their 5th birthday. Gloucestershire Local Authority’s policy is for all children to start school in the September of the academic year in which they become 5 (which means some children will only have just had their 4th birthday when they start school in September).
Parents need to contact the school of their choice early in the Autumn term of the year before their child is due to start school. By March, the Local Authority will write to parents offering places (you have the right of appeal if you are not happy with their offer). By May, all places are allocated.
There is a range of information available for parents to help you choose a school (Ofsted Reports, Performance Tables, etc.), but the most useful source of information is to talk to other parents, then visit the school.