Children and adults often have difficulties comparing decimal magnitudes. Although individuals attempt to reconcile decimals with prior whole-number and fraction knowledge, conceptual and procedural differences between decimals and prior knowledge of whole numbers and fractions can lead to incorrect strategies. The dynamic strategy choice account has proposed that saliency, recency, prior knowledge, and other factors contribute to strategy use when reasoning about decimals. We experimentally tested this theory using a priming technique to manipulate the saliency of different strategies prior to completion of a decimal magnitude comparison task. We hypothesized that whole-number priming (practicing whole-number comparisons with feedback) would increase whole-number bias in decimal comparisons (treating decimals with more digits as larger in magnitude), whereas fraction priming would increase fraction bias (treating decimals with fewer digits as larger in magnitude). We also explored participants' performance in decimal comparisons after being primed by decimal comparisons with feedback. Sixth to eighth graders (N = 149) and adults (N = 175) were randomly assigned to 1 of 4 priming conditions: whole-number, fraction, decimal, or a control (flanker) task. Participants first completed numerical magnitude comparisons according to their priming condition (or control task) with feedback, then all conditions completed decimal comparisons without feedback. In both children and adults, fraction priming significantly reduced whole-number bias compared with the control. Among children, fraction priming significantly increased fraction bias. Moreover, children's performance in the control and whole-number-priming conditions was characterized by strong whole-number bias, but in the decimal-priming condition, relatively brief feedback substantially improved decimal comparison performance.