Teachers underwent two days professional development in CGI. The content of the professional development sessions was drawn from activities and materials set out in the CGI Workshop Leaders manual. The sessions adhered to the recommended sequence by introducing frameworks of addition and subtraction problem types and children's solution strategies related to these problem types. These frameworks form a basis for understanding children's mathematical thinking. Due to the limited time available professional development was restricted to addition and subtraction. It was deemed more useful to cover content in depth rather than adopting a wide and shallow approach.