The present study tested whether a reduced number of categories is optimal for assessing mathematics self-efficacy among middle school students using a 6-point Likert-type format or a 0- to 100-point format. Two independent samples of middle school adolescents (N = 1,913) were administered a 24-item Middle School Mathematics Self-Efficacy Scale using either a 101-point or a 6-point response scale format. The findings suggest that the two different response scale formats were optimally represented by a 4-point scale and supported when samples were pooled. Results provide tentative evidence that middle school students make use of only 4 scale points and that the items on this scale are best matched with adolescents with average to below-average mathematics self-efficacy. Implications for the measurement of self-efficacy and related motivation constructs are discussed, and replications with a 4-point scale using category descriptors for each scale point are needed.