Mathematical play has a fairly short history, with strong roots further back in time (e.g., Papert, Montessori), and understanding the role of mathematical play from early childhood to adulthood is, as yet. unmapped. This working group will build on the success of last year's working group and continue to provide a community space to explore and discuss mathematical play broadly, ranging from informal to formal contexts and from 3rd grade students to teachers in professional development. We will emphasize physical and digital interactions designed specifically to support mathematical play. Each day will focus specifically on a different approach to and definition of mathematical play. Day 1 will focus on mathematical play and making by 3rd to 5th graders across formal and informal environments; Day 2 will focus on intellectual play within mathematical microworlds; and Day 3 will focus on mathematical play in teacher professional development. Throughout the sessions, we will be examining threads of common ground that will assist in developing a more flexible and appropriate model of mathematical play that can inform design of environments and activities across age groups, content, and context. [For the complete proceedings, see ED606556.]