Young people often are asked what they want to be when they grow up. How do their aspirations change as students move through childhood and adolescence? To investigate the formation of career aspirations, we analysed 6308 questionnaires from 4213 students aged 8 to 18 years arranged in an accelerated longitudinal design. Using a person-centred analytic approach, a latent class mixture model identified four discrete change trajectories in the prestige levels of career aspirations over ten schooling years. In line with Gottfredson's (J Counsel Psychol 28(6):545-579, 1981) theory, significant factors included student gender, education aspirations, prior achievement, knowledge of educational pathways to occupations, and the sex composition of occupations. High aspiring students with low education aspirations and poor achievement had more volatile trajectories than other students, regardless of socioeconomic status. The results demonstrate complexity in the formation of aspirations and challenge conventional notions about the 'types' of students who have 'high' and 'low' aspirations.