There are days where I laugh at the idea of a bachelor's degree meaning anything. Usually days where I've been heavily exposed to undergrads.
My advisor has long had an open policy of inviting undergraduate students to conduct honors theses in our lab. My first year here, there were no less than five seniors doing so. After that, with the sudden proliferation of graduate students in her lab (four of us), mentoring undergrads through a senior thesis became part of the undergraduate student training. Not that my advisor forces us to do it; some of us volunteered when s/he became too busy to manage additional students, and now it's become The Way.
The problem is that none of us are exactly eager to mentor undergrads at this point. There have been a variety of...failed or near-failed mentoring experiences. There was the project where we ended up kicking the student out of the lab (or, in lab coordinator terms, "we are going to ask you to leave the lab, yes") for complete dereliction of duty, as our Worst Case Scenario. I am supposed to be helping an undergrad through her thesis defense right now, as a matter of fact, but after a semester of showing up to meetings she wouldn't show up to, holding her hand through such simple things as calculating means in Excel, and asking for progress reports that never got sent, we sat down and asked her if she was really dedicated to this "thesis" thing. She wasn't, and left the lab. There isn't really a problem with this, I just would have preferred to find out earlier. A lot earlier.
On the other hand, mentoring can be very rewarding. Last year I mentored a high school student, who went on to win the local science fair with her project and advanced to the state level. She came here for college, and is now a regular member of the lab. It's not quite a gold standard - it was a poster presentation, not a written thesis and verbal defense - but it helps me remember why I agreed to mentor in the first place.
There isn't really a good way to filter undergrads when they ask to do a thesis. Our lab has an application process, including references and resume and two interviews. We do manage to avoid the most ridiculously incompetent undergrads, but recently we have had a remarkable lack of success figuring out which undergrads are here to bolster resumes or graduate with honors rather than actually being committed to whatever project they undertake.
This year there are four juniors who want to take up a senior thesis project for next year. Four undergrads, four grads. No pressure; it's just that if any of us can't or don't want to take on mentoring responsibilities for next year, one of our dedicated RAs will be SOL. With this pressure, we have collectively revamped the process by which undergrads are accepted into an honors thesis and matched to a graduate mentor.
The key idea we hope to promote is independence, or at least self-sufficiency. Mentoring undergrads who turn to you when they can't figure out how to copy and paste data is more work than we have time for. We also want dedication: students who know how much work a thesis will take and aren't going to quit because they would rather spend their time at choir practice. And, of course, we want to train them on the skill sets they will need, which are supposed to be what makes the thesis worth the laudes.
So we're developing a pre-thesis course, required for thesis hopefuls and optional for anyone else in the lab who might find it worthwhile. There are two parts: statistics and writing. The statistics workshop will introduce students to our stats package (a needed refresher for later analysis) and also test independence with an assigned analysis project to see if students can turn training into knowledge with a minimal of fuss. The writing workshop will provide a basic measure of writing and analytical skills (reviewing a journal article, probably). By these workshops combined, we will test dedication. If you sit through all these requirements, you must really want to do a thesis despite pressures on your time.
Whether this actually weeds out any thesis hopefuls, or we will be faced with the pressure of not wanting to deny thesis chances to anyone, remains to be seen. At the least, I'll be less apprehensive about my presumptive role as mentor for having some idea of what the undergrads can and will do.