Complex sentence: Thrapston Primary is for years 4 to 9 and King John is for years 9 to 13, after which children go to schools elsewhere, usually Prince William School in Oundle.
Split into simpler sentences: Thrapston Primary is for years 4 to 9 and King John is for years 9 to 13. After this children go to schools in different places, usually Prince William School in Oundle.