This paper describes the longitudinal impacts of a partnership between the University of Colorado Boulder's K-12 Engineering Education initiative and the St. Vrain Valley School District. Together, university and high school educators created a replicable pre-college engineering model in a nine-school feeder system, which serves many Colorado students who are traditionally underrepresented in the engineering profession, and culminates with a high school STEM (science, technology, engineering, and mathematics) Academy whose graduates are motivated to thrive in engineering colleges. However, the following question, "Is this an effective model for increasing student STEM persistence and performance?" remains a driver for our investments as we refine the K-12 engineering program based on partner school feedback and quantitative and qualitative assessment results. Data show that our K-12 engineering program has positively impacted student perception, preparedness, and persistence in engineering based on regular, pre-college hands-on engineering design experiences. A description of the multi-year K-12 engineering model and longitudinal analysis of students' concurrent math course choices is presented. Also, subsequent student persistence in and from the STEM Academy is addressed.