This report describes a cluster randomized control trial (RCT) intervention study of the effectiveness of the ABRACADABRA (ABRA) Web-based literacy system using a classroom-level RCT intervention with 1,067 children in 74 kindergarten and Grade 1 or Grade 1/2 classrooms across Canada. The authors closely followed the CONSORT criteria for executing and reporting high-quality RCT studies. Welltrained teachers delivered the ABRA intervention to their regular classrooms for 20 hr per child over one full semester. At posttest, the ABRA intervention classroom showed significant advantages over controls in phonological blending ability, letter-sound knowledge and, marginally, for phoneme segmentation fluency. A secondary analysis exploring the effects of different levels of program implementation showed that with fidelity of implementation (80% of intervention teachers), advantages were evident at posttests in phonological blending, phoneme segmentation fluency, sight word reading, and letter-sound knowledge. It is concluded that ABRA is an effective resource for key skills associated with early reading. Implications for the role of both Web-based technologies and extended professional development for technology in aiding in the scale-up of evidence-based reading interventions are discussed.(author abstract)