Supporting students' additive thinking: The use of equal additions for subtraction

How can teachers support students' additive thinking? This article focuses on the study of a lesson designed to teach the equal additions strategy for subtraction, in which many teachers, despite having a strong commitment to promoting conceptual understanding, struggled with various aspects of the material and resorted to teaching procedurally. The authors conclude that teachers need to have a deeper, more connected understanding of addition and subtraction in order to develop their pedagogical content knowledge in mathematics.