ABSTRACT BACKGROUND School is an important setting to promote healthy eating habits for children. We compared the effects of 4 conditions on the nutritional quality of snacks brought to school. We also investigated teachers' opinions regarding the process, barriers, and facilitators in regulation implementation. METHODS We compared the nutritional quality of morning snacks based on 1958 photographs from schools divided into 4 conditions: regulation based on a list of permitted foods and beverages; regulation banning sweets, chips, and sugary drinks; information without regulation; or no intervention. Based on 5 focus groups (N = 18 participants), we investigated factors influencing regulation implementation. RESULTS In schools with a list of permitted foods and beverages, 76% of the children had a healthy snack, compared to 52% to 54% in the 3 other conditions (p < .01). They also brought less sweet foods compared to those in the other conditions (41% vs. 68% to 71%, p < .01). In focus groups, most teachers supported regulation but also expressed ambivalence about their legitimacy. CONCLUSIONS In this study, a regulation based on a list of permitted foods and beverages showed the best results. All actors should be involved in a progressive implementation process to increase acceptance of such regulation.