The Department for Education has provided guidance for Key Stage 1 and 2 in maths. https://www.gov.uk/government/publica... identifies core concepts in the national curriculum, and shows how pupils can progress their understanding of them over the course of primary school.

Their series of videos introduces the guidance and summarises the core concepts for each year group.  Here you can watch the specific guidance for Year 3 and Year 4.

Year 3

Year 4