Interpreting change in Body mass index (BMI) among youth by comparison to growth charts can be difficult because of maturation-related changes. The aim of this paper was to evaluate the utility of several alternative methods for assessing change in BMI among children. Participants included 1,615 children measured for stature and body mass in first grade and then again the following year. A total of 1,101 students were also assessed in eighth grade. Change was examined using BMI percentiles (BMI%), BMI z-scores, "Percent Over BMI" (BMI50), and the Healthy Fitness Zone continuum, also referred to as BMI85. Youth at lower BMI levels at baseline showed a positive mean change in BMI%/z-score, whereas those at higher levels at baseline showed a negative mean change in BMI%/z-score. These patterns were not seen with BMI50 or BMI85. Assessing change in weight by using BMI% may result in bias so researchers are encouraged to use BMI85 as a more appropriate approach.