The purpose of this study was to evaluate the impact of Achieve3000, a differentiated online literacy curriculum, on students' scores on the California State Test (CST). In the 2011-12 school year, 1,957 students in Chula Vista began using Achieve3000's solutions in 3rd through 8th grade. Using a form of propensity score matching called Inverse Probability-of-Treatment Weighting (IPTW), the researchers assigned weights for the likelihood that students in the non-user comparison group (N = 7,598) could have been in the Achieve3000 treatment group. A Weighted Least Squares (WLS) regression model with IPTW weights estimated the average treatment effect. The researchers found that, overall, the students assigned to Achieve3000 performed statistically significantly higher on the CST, by 2.4 points, than students who were not using these solutions. This suggests the program is effective in improving student learning over conventional classroom activities in the first year of use, however more data is needed to determine the long term impact of usage. Five appendices contain supplemental tables and figures.