The purpose of this study was to evaluate the effectiveness of code-oriented supplemental instruction for kindergarten students at risk for reading difficulties. Paraeducators were trained to provide 18 weeks of explicit instruction in phonemic skills and the alphabetic code. Students identified by their teachers meeting study eligibility criteria were randomly assigned to 2 groups: individual supplemental instruction and control. Students were pretested in December, midtested, and posttested in May-June of kindergarten. At posttest, treatment students significantly outperformed controls on measures of reading accuracy, reading efficiency, oral reading fluency, and developmental spelling. Treatment students had significantly higher linear growth rates in phonemic awareness and alphabetic knowledge during the kindergarten treatment. At a 1-year follow-up, significant group differences remained in reading accuracy and efficiency. Ethical challenges of longitudinal intervention research are discussed. Findings have policy implications for making supplemental instruction in critical early reading skills available.