The current research aimed to study mind wandering and its two dimensions (intentional and unintentional) and learning retention during the lectures and throughout the semester, as well as to study the relationship between mind wandering and its two dimensions and learning retention. The sample consisted of 65 students (4 males and 61 females) in the third year at Faculty of Education - Zagazig University (mean age = 21 years and 8 months, standard deviation = 0.27). The research was conducted during the teaching of the experimental psychology course. Mind wandering was measured using probes over three lectures, and learning retention was measured through the learning retention test consisting of three subtests given at the end of the three lectures. The results showed an increase in mind wandering and its two dimensions (intentional and unintentional) during the lectures, an increase in intentional mind wandering and mind wandering (total degree) during the semester, a decrease in learning retention during the lecture, and learning retention reaching its highest levels during the middle of the semester. Finally, there were statistically significant negative correlations between mind wandering and its two dimensions and learning retention.