Abstract—While Computer-Assisted Instruction (CAI) has been shown to positively impact learning outcomes in the short-term, longitudinal research has demonstrated that gains diminish with time. It is important for research to demonstrate that this increasingly prominent technology is preparing young students for successful scholastic careers. The current longitudinal study explored the long-term impact of an adaptive CAI program on young students’ literacy skills. Two cohorts of elementary school students used Waterford Early Learning (WEL) in kindergarten, first grade, or both kindergarten and first grade during the 2015-2016 and the 2016-2017 school years. The Developmental Reading Assessment (DRA) was administered to students at the end of the 2016-2017 and 2017-2018 school years when students were in first or second grade. Scores of students in both cohorts who used WEL only during kindergarten or first grade (for one year only) or in kindergarten and first grade (for two years) were compared to scores of students who received traditional, teacher-directed classroom instruction. Analysis indicated a salient and persistent effect of CAI: One to two years after students stopped using the program, students who used WEL for one or two years outperformed students who did not use WEL. Additionally, evidence was found for a dosage effect: While all students who used WEL had higher end of year scores than students who did not use WEL, the largest effects were found for students with high CAI usage. The findings of the current study extend prior research which had found that better results within a single school year could scale with increased use of CAI. Given the evidence found for both a lasting benefit and a dosage effect, the current study endorses the sustained use and early implementation of CAI.