Students’ units coordination activity: A cross-sectional analysis

•Growth from units coordination Stage 1 to 2 is tied to iterating composite units.•Growth from Stage 2 to 3 is tied to increased flexibility in working with units.•Conflating units indicates attention to additional levels of units.

Students’ ability to coordinate multiple levels of units constitutes a cognitive core in their mathematical development across several domains, including counting, whole number multiplication, integer addition, fractions concepts, and algebraic reasoning. Identifying a progression of students’ units coordination activity would help educators leverage and support student development within and across the three stages of units coordination. This paper contributes to that goal by describing a cross-section of units coordination activity observed during pairs of clinical interviews with 47 grade 6 students. Results include a 36-rank scale of units coordinating activity with accompanying characterizations and descriptors.