Objective: Health-related fitness knowledge holds the potential for physical activity and behavioural changes. The purpose of this retrospective longitudinal study with retrospective data was (a) to examine high-school students' health-related fitness knowledge growth through the 9th, 10th and 11th grades under one curriculum condition and (b) to examine gender- and school-level correlates of students' health-related fitness knowledge and its rate of growth. Method: This study used existing data collected by school districts as they implemented the curriculum. Participants were students (n = 9,883, 49.4% girls) from 40 high schools following the same curriculum. Health-related fitness knowledge performance was assessed annually for 3 years using an online platform. Potential student- and school-level correlates were collected. A three-level hierarchical linear model was used to examine student health-related fitness knowledge growth and its relation to gender- and school-level correlates. Results: The results showed that high-school student health-related fitness knowledge growth was linear during the 3-year period, with an estimated growth rate of 9.14 ± 1.40% per year under the curriculum condition. Girl students had a higher growth rate than boys, holding other factors constant. Other school-level variables were not significant predictors of health-related fitness knowledge. Conclusion: Overall, the curriculum context was conducive to student health-related knowledge growth. The different knowledge growth rate between boys and girls was a possible reason for gender discrepancy at the 11th grade.