We investigated the cognitive process of 45 beginning students, advanced students and experienced teachers who responded to selected items from Arizona Educator Proficiency Assessment (AEPA) practise tests while they were thinking aloud, AEPA is a licensure test required of all applicants for a teaching certificate in Arizona. Our attempt was to understand the types of mental processes used in taking these kinds of tests. We wanted to discover which mental process was the most frequent, if there were any mental processes related to performance on the test and if there were any differences between the three groups attending our study. Deciding about option was the most frequent thought process among the participants. Common sense was the only significant positive predictor related to test score. Error was a significant negative predictor in predicting test scores, which demonstrate that higher performers tended to rely less on test irrelevant strategies. Further we found differences between the three groups’ mental thought processes. Advanced students tended to rely more on processes based on learning theories and research, experienced teachers drew more on processes based on own experience, and beginning students had a higher proportion of mental thought processes based on error.