Knowledge checks: an apparently successful assignment

Unlike most folks my semester doesn't start for another few weeks, so this week I'm doing general planning for next semester and analyzing student feedback from last semester. I just got finished looking at data from last semester's Zoology lecture, and one assignment, weekly knowledge checks, stood out from the rest. Here's why:

97.8% of students said the knowledge checks either "helped a little" or "definitely helped" them understand the course material, while only 2.2% said that the assignment was "no help at all" (63% answered "definitely helped"; 34.8% answered "helped a little").

89.1% of students "would prefer the course with knowledge checks," while 8.7% "would prefer the course without knowledge checks" (2.2% were "not sure / intermediate").

(data based on voluntary in-class anonymous surveys distributed at the end of the semester, n=47)

Considering that the knowledge checks were an assignment that took at least half an hour outside of class each week to complete (and many students spent much more time than that), I consider that to be pretty good feedback.

Knowledge checks are essentially weekly review quizzes that I administer online using course management software (WebCT, though others like Blackboard would work). I post each knowledge check after my last lecture of the week, and each student must complete that knowledge check by the start of next week's lecture (they have ~5 days to complete them including a weekend). As a concession to possible technical or other problems I drop their lowest two grades. The knowledge checks end up being worth 120 points out of ~500 points possible for the course. The questions are based primarily on my lecture, and focus on comprehension of terminology and basic concepts.

What differentiates knowledge checks from typical weekly quizzes is that I allow each student to take each knowledge check up to 5 times, and only record their highest score. After each attempt the student can immediately see how many points they got, both for the entire knowledge check and for each question (the latter is essentially a "right" or "wrong" indicator, though for multi-part questions this gives an idea of what proportion of answers they got correct). The knowledge checks are open book and open note, and the students can spend as much (or as little) time as they want on them.

My main goal with the knowledge checks is to encourage students to keep up with course content; I don't think of them as a tool to evaluate individual student comprehension (I feel papers and tests better fill that role). The majority of students get 90-100% correct on the knowledge checks, and almost all students retake each knowledge check multiple times to achieve as high a score as they can. I know that many students view the knowledge checks as "free points," though I suspect that this belief motivates students to work harder on the assignment (e.g. "I want to make sure I get a 10!") and thus helps the assignment achieve its pedagogical goal.

I quite enjoy having knowledge checks in the course; they motivate student questions (and office hour visits), help keep the students up-to-date with the material, and give me weekly feedback about how well students have grasped various topics. In fact, I typically start each week's lecture by discussing any recent knowledge check questions that students had significant trouble with.

I'm curious what suggestions/comments folks have on this assignment, as well as what other types of coursework people use to keep their students up to date on lecture material.