Objective: The objective of this study was to assess the association between knowledge, attitudes and practice of oral health in 12-year-old schoolchildren, and to analyse the findings in terms of the conventional KAP health-education model and of the critical approach. Study design: This study has a cross sectional design. The study participants were 1105 randomly selected 12-year-old children resident in the region of Galicia in Spain. For data collection, five teams of one dentist and one assistant were formed. The dentist carried out the physical examination and the assistant helped the subjects to answer the questionnaire. Knowledge, attitudes and practice were assessed, as well as oral health indicators. Multiple regression analysis was used to identify variables affecting practice (as measured by extent of plaque). Results: The results of this study show how that there is an important association between oral health knowledge, attitudes, and practice in 12-year-old schoolchildren in this region. However, the results also show that attitude is not totally explained by knowledge, so that attitude cannot be understood simply as an intermediate variable in a knowledge? practice causal chain. Specifically, the results indicate that sociocultural environment modifies the association knowledge, attitudes and practice. Conclusions: Within oral health education it is clearly important to increase public knowledge of the risk factors for dental disease. However, the efficacy of such education will be limited if health programs do not directly impinge on attitudes, and take into account factors related to the environment, education, social status and economic level of the targeted population.