Research Findings: This study reports on the outcomes of a multisite, two-tiered, response-to-intervention instructional model for delivering phonological awareness instruction and intervention to kindergartners. Fifty-seven kindergartners from 3 classrooms participated in a supplemental phonological awareness program, and 56 kindergartners from 3 classrooms received the prevailing school-adopted literacy curriculum. All children in the supplemental condition received supplemental classroom-based phonological awareness instruction in addition to the adopted literacy curriculum. At mid-year, 6 low literacy achievers were identified in each supplemental classroom (n = 18) to participate in an additional 12-week small-group intervention. The classroom-based supplemental curriculum did not produce statistically significant gains for typically achieving children on measures of letter-sound knowledge, word recognition, or developmental spelling. However, an add-on tier of supplemental instruction exerted a substantial advantage for low-achieving children on a measure of developmental spelling. Practice or Policy: Results suggest that a 2-tiered intervention model provides an effective means for improving the literacy outcomes of low-achieving kindergarten children. (Contains 3 tables and 2 footnotes.)