@inproceedings{sztajn_campbell_yoon_2009, title={Conceptualizing professional development in mathematics: Elements of a model}, volume={5}, booktitle={Pme 33: proceedings of the 33rd conference of the international group for the psychology of mathematics education, vol 5}, author={Sztajn, P. and Campbell, M. P. and Yoon, K. S.}, year={2009}, pages={209–216} }