Studies show that extending students' mathematical thinking during whole-group discussions is a challenging undertaking. To better understand what extending student thinking looks like and how teachers' mathematical knowledge for teaching (MKT) supports teachers in their efforts to extend student thinking, the teaching of six experienced elementary school teachers was explored. During group discussions, all six teachers created opportunities for extending student thinking about important mathematical ideas and solution methods. Findings on the nature of these episodes include identification of individual instructional actions and the ways in which teachers' MKT was connected to these actions.