This document presents a review of evidence commissioned by the Education Endowment Foundation to inform the writing of the guidance report "Improving Mathematics in the Early Years and Key Stage One" (ED612298). The review aimed to synthesise the best available international evidence regarding teaching and learning of mathematics for children in Early Years and Key Stage 1 (i.e., between the ages of 3 and 7) and aimed to answer the following research question: "What is the evidence on the effectiveness of classroom-based interventions for improving mathematical learning of children in Early Years and Key Stage 1 settings?"