[Impact of Regulation of the School Food Environment: methodological aspects and participation in the first year of follow-up].

This article describes methodological aspects and characterizes participation in the first year of the study Impact of Regulation of the School Food Environment. The aim was to monitor food sales in and around private school canteen in three Brazilian cities with different regulatory contexts and investigate the perceptions of students with regards to canteen. A repeated cross-sectional study (2023/2024 and 2025) was conducted with independent samples in the cities of Recife (Pernambuco State), Niterói (Rio de Janeiro State), and Porto Alegre (Rio Grande do Sul State). For the Canteen Module, sampling involved private primary schools and high schools stratified by school size and with inverse replacement. A convenience sample was used for the Street Vendor Module and 3-stage cluster sampling was used for the Student Module. The first two modules replicate the method of the Food Commercialization in Brazilian Schools study. The first data collection process took place between September 2023 and May 2024. Two hundred two schools and 532 students participated. Only three street vendors were located. School participation rates were 47.8% in Porto Alegre, 53.9% in Niterói, and 69.9% in Recife. Schools were reluctant to participate in the survey, which prolonged the data collection process. This article discusses the challenges faced during fieldwork and the methodological adjustments required for the second year of monitoring, offering recommendations for future studies in the school setting. This project is the result of a collaboration between academia and organized civil society, which required information to support advocacy for healthy eating at schools. The evidence generated could assist in the formulation and improvement of protection policies for the school food environment in other cities and on other governmental levels.