Research into human decision making (DM) processes from outside of education paint a different picture of DM than current DM models in education. This pilot study assesses the use of critical decision method (CDM)--developed from observations of firefighters' DM -- in the context of primary mathematics teachers' in-class DM. Preliminary results show that CDM yields significant amounts of data regarding teachers' cognition during DM and that the process that expert teachers follow when they make decisions may better match naturalistic accounts of DM.