How to motivate students to complete work that I cannot frequently check? I assign my undergraduate students assignments from a workbook as homework. The homework amounts to about 30-minutes per day.

It is impractical for me to collect these workbooks at each lesson, or even weekly, as any days when I am checking the work are days when the students don't have their workbooks in hand. Furthermore, I cannot constantly collect, carry, and redistribute hundreds of workbooks each week.

As such, I've limited my collections of these to twice per term. The results, however, have not been good. A great many students save many weeks of work until the last minute, only to discover then that the task is far more difficult than they anticipated.

How can I motivate my students to complete work daily when it is impractical for me to frequently assess it?
The other answers are excellent. Without knowing your field or the nature of the workbook assignments, I'll give the following answer:

I have become a big fan of automated online homework systems (although I know some students hate them). If you happen to be in a field where these systems exist (e.g., Physics, Math, Chemistry--WebAssign, MyMathLab, etc.), consider this for a future semester.

The reason I bring up these systems is that (1) they provide a forcing function for the students to do the work, (2) the grading is automatic and immediate, (3) the better systems provide guidance on problem solving, and (4) the math-related problems can be randomized so students can't copy of another student's work (as easily...).



Ideas for your current system:


Do a cursory check of the books every week. By cursory, I mean "check that there is writing on the required pages," and give a check or not. This doesn't preclude them from not putting in much work, but at least they will see that you've got eyes on them each week.
Give them a daily 1-question quiz that is straight from the homework (if it is the kind of work that has "correct answers").
Reassess why it matters that they do the work, and lay it out to them plainly. Do the students who procrastinate on the homework really do more poorly with the material? If the answer isn't an emphatic "yes," then why do you care? If the answer is "yes," then lay this out to them on the first day of class: "I assign the workbook material because it helps you get a better grade in the class. It's up to you to do the work, and your grade will almost certainly reflect the amount of work you put into the workbooks. I don't collect it because I expect you to do it on your own, and it's your grade that matters." In the end, your job is to give them the tools to learn the material, and their job is to use those tools. At the collegiate level, you can expect them to take their education seriously. I.e., "You can lead a horse to water..."