School meals can have a key function in promoting children’s health. However, simply providing a free school meal is not a guarantee that pupils will eat the food. The purpose of this study was to explore factors influencing pupils’ participation in free school meal schemes in Oslo. The study has a qualitative research design, inspired by grounded theory. Data were collected through interviews with pupils, teachers, and parents, and participant observations in two schools participating in a pilot project funded by Oslo Municipality. Line-by-line coding, memo writing, and a constant comparative technique were used to analyze the data. One primary school and one lower-secondary school in different districts in Oslo that were implementing two different free school meal models took part in the study. In total, 39 pupils (5th–10th grade), 15 parents, and 12 school employees were included. Four main factors related to pupils’ participation in free school meals emerged from the analysis: the popularity of the food served, the attraction to the nearby shopping center, social aspects, and predictability. To promote pupils’ participation in free school meal schemes, schools need to solve the challenges of balancing between healthy food and popular but often unhealthy food. To implement school meals further, children and parents’ involvement, regularity of the meals provision, a good flow of information, and the creation of a friendly eating environment are recommended.