This paper examines the effect of participating in a web-based health programme that promotes personal tracking of high school students' own measurements of a number of health-related parameters. Danish cross-sectional survey data were used to examine the effects of the health programme on various health measures. Both quantile regression models and standard ordinary least squares (OLS) models were used to explore the correlations between the students' participation in the health programme and their body mass index (BMI), body fat percentage, aerobic fitness, and well-being. Participation in the health programme increased BMI and aerobic fitness among students with a BMI or an aerobic fitness value ranging from the 25th percentile to the 75th percentile and reduced body fat percentage among students with the highest percentages of body fat. In addition, the health programme led to an increased feeling of wellbeing among students, especially those with high BMI levels and poor aerobic fitness. As the schools participated in the health programme on voluntary basis and at a financial cost to themselves, the positive effects of participation found can only be stated to be valid among students from committed schools.