The main differences between Key Stage 1 and Key Stage 2 are the age range, the focus of the curriculum, and the amount of assessment. Key Stage 1 is for children aged 5-7, while Key Stage 2 is for children aged 7-11. Key Stage 1 focuses on the basics of literacy and numeracy, while Key Stage 2 builds on these skills and introduces children to a wider range of subjects. There are also more assessments in Key Stage 2 than in Key Stage 1.