Creating supportive oral health-related environments in schools is an important strategy for promoting schoolchildren’s oral health. This study determined the associations between school environments and children’s oral behaviour and dental caries. The data on school oral health-related environments were obtained through observation and interviews. Oral behaviour and dental caries data were collected through interviews and oral examinations of 984 sixth grade children. χ2 and multiple logistic regression, adjusted for sociodemographic and economic status, other school environment variables, and oral behaviour were used. Providing fresh fruit with school meals was associated with low sweets consumption and low caries levels. Children’s daily sweets consumption was positively associated with sweetened milk sales in schools. Selling sweetened beverages, including sweetened milk, sweetened drinks, and soft drinks, was associated with high caries levels, while selling meat and crispy packed snacks was associated with low caries levels. Children in schools with integrated oral health education were significantly more likely to brush their teeth twice a day and to brush after lunch. In conclusion, school oral health-related environments, especially available food choices, were associated with sweets consumption behaviour and caries levels. Children in schools with integrated oral health education had better brushing habits.