Higher education institutions are striving to lower student dropout rates to increase the number of academically qualified persons in the labour market and decrease misguided investment. Researchers generally acknowledge that students who are firmly decided on their studies tend to drop out of their studies less frequently. Building on the extended expectancy-value model via the cost component, this longitudinal study investigates changes in and the impact of students’ motivation on career decidedness and intention to drop out. We analysed data from 351 first-year university students aiming to become teachers across three measurement points, finding that the task effort of students and, to a lesser degree, their interest value was related to career decidedness and, indirectly, to the intention to drop out after the first year in higher education. Moreover, the results revealed that these students’ ability beliefs increased and interest value decreased from the beginning to the end of the first year at higher education. Accordingly, we discuss the theoretical and practical implications taken from these findings.