We have investigated the long-term effect of student-centered instruction at the freshman level on juniors' performance on a conceptual survey of Electricity and Magnetism (E&M). We measured student performance on a research-based conceptual instrument--the Brief Electricity & Magnetism Assessment (BEMA)–over a period of 8 semesters (2004–2007). Concurrently, we introduced the University of Washington's Tutorials in Introductory Physics as part of our standard freshman curriculum. Freshmen took the BEMA before and after this Tutorial-based introductory course, and juniors took it after completion of their traditional junior-level E&M I and E&M II courses. We find that, on average, individual BEMA scores do not change significantly after completion of the introductory course--neither from the freshman to the junior year, nor from upper-division E&M I to E&M II. However, we find that juniors who had completed a non-Tutorial freshman course scored significantly lower on the (post-upper-division) BEMA than those who had completed the reformed freshman course--indicating a long-term positive impact of freshman Tutorials on conceptual understanding.