  Standardized assessment tests that allow researchers to compare the
performance of students under various curricula are highly desirable. There are
several research-based conceptual tests that serve as instruments to assess and
identify students' difficulties in lower-division courses. At the
upper-division level, however, assessing students' difficulties is a more
challenging task. Although several research groups are currently working on
such tests, their reliability and validity are still under investigation. We
analyze the results of the Colorado Upper-Division Electrostatics diagnostic
from Oregon State University and compare it with data from University of
Colorado. In particular, we show potential shortcomings in the Oregon State
University curriculum regarding separation of variables and boundary
conditions, as well as uncover weaknesses of the rubric to the free response
version of the diagnostic. We also demonstrate that the diagnostic can be used
to obtain information about student learning during a gap in instruction. Our
work complements and extends the previous findings from the University of
Colorado by highlighting important differences in student learning that may be
related to the curriculum, illuminating difficulties with the rubric for
certain problems and verifying decay in post-test results over time.
