The introductory astronomy laboratory course at the University of Maine consists of weekly lessons in which students work in small groups on computer-based exercises. My work consists of assessing and revising a lesson on astronomical time-keeping, including sidereal time, Apparent Solar Time, and time zones. After a baseline of pretest and post-test data was collected, the lesson went through two major revisions. For the spring 2005 semester, the unit was altered to incorporate planetarium software for simulating the sky instead of the physical celestial sphere models previously used. This change produced only small gains from pretest to post-test, so a more drastic change to the lesson was planned. For fall 2005, the entire lesson was rewritten to focus more explicitly on the desired conceptual content and less on intermediary mathematical manipulations. This final iteration of the material was reused in the spring 2006 semester with a new pretest that was updated based on student interviews. Although the fall 2005 data indicated a trend of pretest to post-test improvement with the rewritten lesson, the spring 2006 data do not sustain this trend. Overall, neither the interface change nor the switch to a more inquiry-based style seem to reliably affect student performance on the post-test. I will present and discuss these results in detail, including possible explanations for the lack of pre/post-test gain.