Dylan's units coordinating across contexts

Units coordination has emerged as an important construct for understanding students' mathematical thinking, particularly their concepts of multiplication and fractions. To explore students' units coordination development, we conducted an eleven-session constructivist teaching experiment with a pair of sixth-grade students, investigating how they coordinated whole number and fractional units in discrete and continuous settings. In this paper we focus on one student, Dylan, who reasoned with whole number units but not fractional units at the beginning of the teaching experiment. We describe Dylan's development of units coordination as he continued to reason with whole number units in fractional situations, and we discuss implications for instruction.