In this review, texts used in the research on which the National Reading Panel based its conclusions in its 2000 report about the role of fluency in reading and its sensitivity to practice were grouped in 4 categories. Three of these text categories (pre-1990 basals, skill builders, and high-interest/low-vocabulary texts) used controlled vocabulary and accounted for approximately 75% of all texts used in the studies reviewed by the panel. When various features of these controlled vocabulary texts were compared with those in current, mainstream textbook programs, the primary difference was the treatment of rare words. Compared to controlled texts, current mainstream textbook programs have substantially more rare words, and approximately 70% of these words appear a single time.