The Knowledge Is Power Program (KIPP) is a national network of public charter schools whose stated mission is to help underserved students enroll in and graduate from college. As of 2014-2015 the network included 162 elementary, middle, and high schools serving 59,495 students. Questions remain, however, about the ability of charter school networks like KIPP to remain effective as they expand and serve larger numbers of students. In this paper, the authors present estimates of the impacts of KIPP middle schools during a period in which the network greatly expanded. In particular, they measure KIPP impacts between 2005 and 2014, a period in which the number of schools in the network increased from 40 to 140. They aim to explore whether there is any evidence of an increase, decline, or stability in KIPP impacts over this period and the extent to which variation in network-wide impacts is driven by changes to the composition of the network versus changes over time in the effectiveness of existing schools. The paper focuses on 37 KIPP middle schools open during the 2005-2014 period in 14 KIPP regions and 11 states. The study sample included a treatment group of students who entered a KIPP school for the first time in grade 5 or grade 6, and a matched comparison group of students in the same school districts who did not attend KIPP. In total, a sample of 20,312 treatment students and 20,312 matched comparison students were analyzed. The study relied on a matched comparison group design that used "nearest neighbor" matching to identify a similar comparison student for each treatment student entering a KIPP middle school in grade 5 or grade 6. Once the matched comparison group was identified, impacts were estimated using ordinary least squares (OLS) regressions that control for any remaining baseline differences between KIPP students and comparison students. The authors used de-identified, longitudinally-linked student-level data from jurisdictions (states or districts) hosting at least one KIPP school and able to provide student-level records at the time of data collection. The study results suggest that KIPP middle schools continued to produce positive impacts on student achievement outcomes even as the organization faced the pressures of growth in terms of student recruitment, hiring new principals and teachers, and managing turnover in the network's workforce over time. Figures are appended. [SREE documents are structured abstracts of SREE conference symposium, panel, and paper or poster submissions.]