Easy to digest research on Mathematics education from Cambridge Mathematics, see their Espresso page where in their words, “Each month we bring you an Espresso – a small but intense draught of filtered research on mathematics education, expressly designed with teachers in mind. Each Espresso considers one particular issue in mathematics education, and how the latest good-quality research can provide helpful guidance or further reading.”
This on Working Memory in Mathematics Learning is an excellent example of the clear and concise communication of research which these Expressos provide.
Craig Barton has an excellent selection of research papers he recommends for teachers. Craig has structured this really clearly as you can see from his Contents.
Craig states that his page contains the academic research he has read that has influenced the way he plans and teaches mathematics.
From the Education Endowment Foundation, see Improving Mathematics in Key Stages 2 (ages 7-11) and 3 (ages 11-14). The Guidance Report offers eight practical, evidence-based recommendations—that are relevant to all pupils— but particularly to those struggling with their mathematics. Note the recommendations summary poster.
For 2019-20120, see Loughborough University Mathematics Education Network.
See also Research – Learning & Teaching. relevant for teachers of any subject.