One of the more surprising things about this job for me has been the difficulty I have had engaging undergraduate students in research. It's not as though I didn't have experience on this front before starting here - I supervised undergraduate researchers as both a Ph.D. student and a postdoc, with good results. Nevertheless, it has taken me some time, not only to recruit the students, but to find the right projects for them. With multiple very different projects happening in the lab, it should be easy to slot the students in, but this is not the case.
Part of the issue is the training. In most cases students who come into the lab need a substantial amount of training before we trust them with working unsupervised. That puts a burden on either myself or the lab member who will be working with them. If they learn quickly and become an asset, the training quickly pays off. But we have had pretty high rate of students who either are not careful enough to be trusted or decide that the reality of this work is not what they thought they were signing up for. It doesn't seem to matter how much I explain what we do, many still seem to be surprised by the work.
So far, the best luck I have had with undergraduates in the lab are those I have brought in early. If I can get them before their third year, not only is the training effort easier to commit to, but they can get engaged at a deeper level in a project. A year or nine months is just not long enough for them to see the forest for the trees. Two years, on the other hand, gets their heads in it enough to see the broader picture and gain more of a sense for why we do what we do. It is also enough time for them to take on their own project, rather than working in conjunction with a grad student to push something to fruition.
It would be interesting to hear what other people do to get undergraduates not just involved in the lab, but engaged in what is going on.