What Works Clearinghouse Intervention Report: Reading Mastery

The What Works Clearinghouse (WWC) reviewed evidence for Reading Mastery among English language learners and found potentially positive effects on reading achievement. The review included one randomized controlled trial conducted in Oregon involving English language learners in grades K–4 who received Reading Mastery as a supplemental reading intervention in addition to their regular instruction. The study focused on 17 English language learners identified as performing below expected reading achievement levels. 

Outcomes examined included oral reading fluency, letter-word identification, word attack skills, reading vocabulary, and passage comprehension. Students participated in supplemental small-group instruction lasting 25–30 minutes per day. Reading Mastery provided explicit, systematic instruction in phonemic awareness, sound-letter correspondence, decoding, vocabulary, comprehension, and fluency.

The WWC concluded that Reading Mastery demonstrated potentially positive effects in reading achievement. Reported improvement indices ranged from +21 to +35 percentile points, with a domain average improvement index of +28 percentile points. Follow-up analyses conducted one year after the intervention found sustained positive effects, including a statistically significant impact on word attack skills. The study met WWC evidence standards and supported Reading Mastery's effectiveness for English language learners.