"INSPIRE" is an Investing in Innovation (i3) development grant funded by the Office of Innovation and Improvement, U.S. Department of Education. "INSPIRE" provides an innovative integrated K-12 STEM pipeline approach focused on STEM course content and instructional redesign. The INSPIRE model was implemented in Cabarrus County Schools (CCS), which is among the largest school systems in North Carolina, serving nearly 30,000 students in 39 schools. The impact evaluation included two studies that examined the effect of INSPIRE on mathematics and science achievement as measured by North Carolina standardized End-of-Grades assessments. The elementary study (Study 1) used a three-year, longitudinal, single-cohort quasi-experimental design (QED) to assess the impact of INSPIRE on math achievement at the end of 5th grade after two years of program exposure. The secondary study (Study 2) used an individual-level, longitudinal, randomized controlled trial (RCT) with blocking by school level and cohort to assess the effects of INSPIRE on math and science achievement at the end of 7th and 10th grades after two years of program exposure. For both studies, we compared the outcomes of INSPIRE students with similar students from schools that did not offer a STEM program. For the elementary study, propensity score matching (PSM) was used to match INSPIRE elementary students and comparison student samples at baseline (on pre-test math achievement scores, gender, minority status, and economically disadvantaged status) and baseline equivalence was established all pre-test assessment measures; this study met What Works Clearinghouse (WWC) Group Design Standards with Reservations. For the secondary study, the overall and differential attrition rates were low based on the WWC attrition standards (WWC, 2017); this study met WWC Group Design Standards without Reservations. The results of the elementary study indicated a statistically significant difference between the "INSPIRE" treatment group and the business-as-usual comparison group on the math achievement outcome. Comparison students reported a statistically significant higher increase in math achievement than "INSPIRE" students. Results of the secondary study indicated no statistically significant difference between the "INSPIRE" treatment group and the business-as-usual comparison group on the math and science achievement outcome. The duration of students' exposure to INSPIRE, fidelity of implementation, alignment between PBL instruction and NC standardized assessments, and contextual factors that might have weakened the intervention strength relative to business-as-usual conditions are discussed as possible factors that account for these findings. The report concludes with suggestions for future research and implications for education policy.