Recently, the literature has repeatedly reported an interesting decrease in science and technology (S&T) among youngsters, and a drop of students choosing professions related to these knowledge areas. This study pursued to assess the interest of primary and secondary pupils in specific fields of S&T and to relate this interest to their predisposition to engage in S&T-related out-of-school activities and their inclination to become scientists in the future. A questionnaire on S&T interests and attitudes was administered to a sample of 1336 pupils. Results show that, overall, the inclination to become scientists was low. However, we found a relationship between pupils' interest in areas of S&T and their predisposition to participate in out-of-school S&T activities, and also between their interest and their inclination to become scientists. Moreover, significant age- and sex-related differences concerning all these aspects were identified. We discuss the importance of acknowledging children's and adolescents' specific interest to promote their participation in S&T-related school activities and out-of-school activities. We also urge that information about scientific and technological careers be disseminated in schools in order to increase students' interest in these areas.