We evaluated the impact of teaching complex grapheme-phoneme correspondences (GPC) derived from the Simplicity Principle (Vousden, Ellefson, Solity, & Chater, 2011) to at-risk poor readers in Grade 2 classrooms, using a two-arm dual site matched control trial intervention. Poor word readers (n = 149) were allocated to either a) Simplicity GPC (n=79) or b) Letter-Name Control (n=70) small group reading programs, and received intervention for 12-15 hours over 12 weeks. Students were matched on baseline reading, language, parent demographics, and observed regular classroom teaching quality. Results of hierarchical data modeling showed advantages for the GPC-group for word reading, pseudoword reading, and sentence comprehension at post-test moderated by pre-test phonological awareness skills. The results provide support for teaching complex GPCs derived from a 'Simplicity Principle' as an approach to intervention for word reading, but suggest that children with low PA need additional supports.