THE PEDAGOGICAL CONTENT KNOWLEDGE OF PRIMARY MATHEMATICS TEACHERS FACING A STUDENT ERROR

Nine Italian mathematics teachers were interviewed about a hypothetical classroom situation where an error in the subtraction in column is presented. The link between interpretation of the error and its remediation is considered as a part of pedagogical content knowledge of teachers that is fundamental to address the instruction if teachers want to consider the student thinking to direct their teaching. All the teachers identified the error and interpreted it in different ways. The remediation is mainly related to the concrete model of subtraction as "take away" that is not connected with the interpretations of the error. Teachers show a great trust in the power of explanation of concrete models of subtraction although the error is about the algorithm in column, but this trust don't put them in good conditions to use their mathematical knowledge in a more effective way.