There is an increasing diversity of educational background of students entering ordinary degree (Level 7) and honours degree (Level 8) programmes in engineering at Dublin Institute of Technology (DIT). Partly as a result, student reasoning about basic electricity concepts often differs from accepted explanations. The paper reports, analyses and reflects on the results of a multiple-choice diagnostic test to assess student understanding of such concepts (developed for U.S. high school and college students [1]) taken, as a pre-test, by four cohorts of first year students, on the same DIT Level 7 engineering programme, from 2008-12 (n=106) and two cohorts of first year students, on the same DIT Level 8 engineering programme, from 2010-12 (n=64). The performance of the student cohorts is similar, and is little influenced by previous exposure to relevant subjects in second level (high school) education. In the 2012-13 academic year, an updated version of the diagnostic test was taken, in a pilot study, by one cohort of first year students on the DIT Level 8 engineering programme; this test was administered as a pre-test before instruction, as a post-test immediately after instruction and as a delayed post-test approximately fifteen weeks after instruction. Results show that there is little improvement in conceptual understanding of d.c. resistive electric circuits, as measured by the test, when pre-test, post-test and delayed post-test scores are compared.