"Improving Mathematics in the Early Years and Key Stage 1" reviews the best available evidence to offer five recommendations for developing the maths skills of 3-7-year olds. Recommendations include integrating maths into different activities throughout the day -- for example, at registration and snack time -- to familiarise children with maths language and make the most of the school day. It also highlights that story and picture books can be a powerful tool for engaging children with basic maths concepts, while board games (such as Snakes and Ladders) are particularly beneficial to developing understanding of numbers. Based on the best available international research -- and drawing on the expertise of teachers and academics -- this report is packed with examples and case studies to support practitioners. [For the companion report "Improving Mathematics in Key Stages Two and Three. Guidance Report," ED612294. This guidance is also informed by a practice guide created by the What Works Clearinghouse "Teaching Math to Young Children" (ED544376).]