This qualitative case study investigates how, and to what extent, primary school teachers notice students' mathematical thinking in the context of whole number subtraction. A task involving a student's invented strategy was used to collect data. Three noticing questions connected to the task were asked to 45 teachers. Their written answers were analyzed to reveal teachers' noticing skills based on attending, interpreting, and deciding how to respond. The study results revealed that most participants provided limited evidence of attending and interpreting skills, and some responses showed a lack of evidence. More specifically, they could not identify the relationship between digits in ones and tens places. Further, their interpretations did not directly focus on students' solutions and consisted of general statements and misconceptions.