Three central Virginia school districts and engineering education researchers at the University of Virginia were awarded an Investing in Innovation development grant to design, implement, test, and nationally disseminate a project-based engineering curriculum for middle school students. Referred to as invention kits, the curriculum is developed to teach key science and engineering principles and related skills to Grades 7 or 8 students by constructing modern interpretations of 19th-century inventions that sparked industrial activity within society: the solenoid, the linear motor, and the linear generator. As part of the external evaluation, American Institutes for Research (AIR) conducted an impact study to assess the invention kits' effect on students' engineering and physical science knowledge, as well as students' interest and confidence in STEM learning. The study used a quasi-experimental comparison group design investigating differences in student pre- and-posttests during the 2017-18 school year. Students in four schools across the three districts used a set of three invention kits in their engineering electives, as compared with students taking engineering electives in three schools within one district that had business-as-usual engineering curriculum. AIR studied implementation of the kits by collecting data reported by teachers on student use of kit components, interviews with teachers on how kits were incorporated into their engineering elective curriculum and adapted for use with their students, and observations of kits in use during site visits. The research team did not find a statistically significant difference between the physical science and engineering assessment scores of students who used the kits and comparison students. The research team did not find a statistically significant difference between the measures of STEM interest and confidence of students who used the kits and comparison students. Teachers and students in two of the four schools in the treatment group implemented the three invention kits with fidelity (defined as with at least 75% of their students, using at least 60% of kit components). One of the three kits (Solenoid) was implemented with fidelity by all four participating schools.