It depends on what curriculum you choose to go with. (eg : US or British)

This may not be exact, but will give you an idea though

0-4 UK- Preschool
4-5 UK- Reception
5-6 UK- KS1
6-7 UK- KS1
7-8 UK- KS2 etc


4-5 US-PreK
5-6 US Kindergarton
6-7 US grade 1

Where are you coming from?