Previous research suggests that there are differences in the way various professionals reason. This is evidenced by variable susceptibility to cognitive reasoning fallacies. This study examines these differences between lawyers and doctors through a battery of cognitive reasoning measures including the CRT, Numeracy Scale, Linda Problem, Wason Selection Task, and Beads Task. Secondly, this study aims to pinpoint when these differences emerge in each respective professional track—prior to the onset of training vs. later during professional practice--as a way to discern a self-selecting bias when it comes to thinking styles and career choices. We found that while not ubiquitous, there was evidence to suggest both loci. For certain cognitive aspects in legal education it seems that more schooling leads to improved performance in various forms of reasoning. However, this did not hold true for medical education, which seemed to have relatively little effect on performance. Generally, lawyers were able to score higher than doctors on our battery of cognitive tests, which suggests either that medical professionals are not able to make decisions as soundly, or that this study was unable to reveal the areas of cognitive functioning in which doctors excel over lawyers. Results from this study should be extended by future research that examines more closely the differences revealed here, to better understand how professional education affects decision making.