Students' expectancy-value beliefs play an important role in shaping their educational choices and behaviors. Drawing on Eccles and Wigfield 's (2020) situated expectancy-value theory, we investigated short-term changes in students' expectancy-value beliefs in gateway math courses for beginning university students. In Study 1a, we collected data from first-semester students in three math-intensive study programs at the beginning, midpoint, and end of the semester (N = 1,004). Latent change score analyses revealed a significant decline in students' expectancy, intrinsic value, and utility value, and an increase in perceived psychological and effort costs over the first half of the semester. These maladaptive motivational changes predicted students' end-of-term study program satisfaction, exam performance, and course dropout. Study 1b then explored weekly motivational changes in the very first weeks of the semester using a subsample from Study 1a (N = 773). We found that students experienced a "motivational shock" between Weeks 2 and 3 of the semester coinciding with their first performance feedback on mandatory math worksheets. The motivational shock was characterized by a rapid decline in students' intrinsic and utility values, and a significant increase in their perceived cost. Like Study 1a, the motivational shock in Study 1b predicted students' end-of-term study program satisfaction, exam performance, and course dropout. Across both studies, female students and students with comparatively lower prior achievement experienced more negative motivational changes. Our studies underscore the importance of considering short-term motivational changes as early warning signs of academic struggles and course dropout in math-intensive fields.