Six instructional assistants taught the Early Reading Intervention (ERI) curriculum to 38 at-risk kindergarten students, and 32 nonrisk students served as comparisons. Student risk was determined based on performance on the "Dynamic Indicators of Basic Early Literacy Skills" subtests of Nonsense Word Fluency, Letter Naming Fluency, and Phoneme Segmentation Fluency (PSF). The Word Attack (WA) and Letter-Word Identification (LWID) subtests of the "Woodcock-Johnson III Tests of Achievement" were used to confirm risk status and also as pre- and posttest measures. Treatment students received between 6.85 and 13.70 hr of instruction, with varying degrees of treatment quality. Multiple linear regression was used to analyze the amount of variance in gain scores that could be explained by participation in ERI, treatment quality, and treatment duration. Results showed WA and LWID gains with large effect sizes for treatment students. Findings for treatment quality and duration were mixed, without clear indications of their effects on gain scores. (Contains 5 tables and 4 figures.)