The primary school mathematics curriculum in Ireland is based upon a constructivist philosophy of learning. As constructivism is a theory of learning and not teaching, implementing a constructivist approach in the classroom requires teachers to identify the implications and applications of constructivist philosophy for teaching. In this research, case study is employed to reveal the extent to which teachers' detailed understanding of emergent constructivism and its implications for classroom practice informed their teaching practices, all within the context of teaching problem-solving lessons in the senior primary school mathematics classroom. Results highlight the challenges and opportunities faced by primary teachers as an attempt is made to allow an understanding of learning from an emergent constructivist perspective inform teaching practice. Throughout this research, it emerged that teachers' beliefs and attitudes regarding appropriate mathematical constructions did not correlate with what students may have deemed appropriate. Teachers need to understand their beliefs and those of their students and to work on changing both if necessary. The study affirms that teacher knowledge, beliefs, identify, school contexts and school curriculum are all important factors to consider.