This study tracked health-related physical fitness in 11 year-old youths over their three-year middle school period. The Fitnessgram test battery was administered four times to 116 boys and 129 girls in the US during the period. Results indicated that BMI and estimated %BF tracked best, followed by PACER, sit and reach, push-up, and curl-up. Fitness levels in the estimated %BF and curl-up in the least fit quartiles (at baseline) tracked better than those in the fittest quartiles, and initially at-risk youths had higher probabilities of falling into at-risk categories three years later than those initially in healthy groups. In addition, boys became healthier in the estimated %BF and girls tracked poorer than boys in the PACER. Further, the numbers of girls in the at-risk categories increased considerably in four fitness measures (estimated %BF, BMI, PACER, and push-up) during the middle school period, whereas boys' corresponding numbers either dropped or did not change in all the fitness measures.