Di Siemon has been involved with mathematics teacher education for over 30 years. As a Professor of Mathematics Education at RMIT University she has led a number of large-scale research projects focussed on the development of number ideas and strategies in years F to 9 with a particular emphasis on the use of performance-based assessment tasks to identify learning needs and inform teaching. She is currently leading a research team that is working with 32 secondary schools nationally to develop an evidenced based teaching and learning framework for mathematical reasoning.