This paper shows some of the results of the research conducted with the purpose of knowing the Bayesian reasoning of college students doing their first course in probability and statistics. For this there three tests that were designed and implemented at different times during the semester. The results showed three stages in the reasoning of the students: the first, which coincides with the first test, is characterized by the use of mathematical arguments proportions; the second, which coincides with the second test is characterized by the joint use of tree diagrams and algebraic expression of Bayes which had been taught by teachers; the third, which coincides with the third test, is characterized by the failed recall Bayes rule and incomplete use of the tree diagram attempt.