A report by the What Works Clearinghouse (2012) posted in July 2012 examined two studies of the use of Reading Mastery with students with learning disabilities and concluded that the program had “no discernible effects on reading comprehension and potentially negative effects on alphabetics, reading fluency, and writing.” This conclusion is in stark contrast to dozens of studies of Reading Mastery and other elements of the Direct Instruction (DI) corpus of material. This technical report documents significant errors in the WWC report. The WWC analysis was based on only two articles. One compared two very similar Direct Instruction programs, Reading Mastery and Horizons, and found that students in both programs made gains over the academic year that were significantly greater than those made by students in national and state level populations. Gains in both programs were similar, leading the WWC to conclude that Reading Mastery was no better than its comparison program. They ignored the fact that students performed significantly better than the national or state norms or that the comparison program was similar on all but a very few characteristics. The second article reviewed involved two groups of students, both of which received Reading Mastery as part of the schools’ “usual and customary school day curriculum.” One group of students also received 45 minutes of supplemental phonemic related instruction from their regular classroom teachers. Not surprisingly, the group receiving the additional instruction had significantly larger gains than those who did not have additional learning time. Despite these differences in exposure and the fact that both groups appear to have had Reading Mastery as their usual reading curriculum, the WWC used these results to suggest that Reading Mastery could have potentially negative effects.