This article reports on the student achievement outcomes for third graders in Reading First (RF) schools in Pennsylvania over the five years of implementation for the group as a whole, for disaggregated groups of third graders, and for third graders who received reading instruction in RF schools for one, two, and three years. We also present a school-level growth measure for representing school improvement and for characterizing the success of RF in Pennsylvania. Results indicate that third-grade students in these RF schools are making substantially more progress in third-grade reading than are students in other schools in Pennsylvania, there is an increase of nearly 24% of students performing at proficient or advanced level over the five years, and the students in the below basic range on the achievement measure declined nearly 18%. Further, the disaggregated data show that the achievement gap, though not closed, was reduced for all groups of third graders. Finally, nearly 80% of the RF schools were successful in accomplishing the two goals of Reading First: an increase in the percentage of students at grade level, and a reduction in the percentage of students who were seriously below grade level. (Contains 6 tables, 3 figures and 2 notes.)