The graduate institution that I am on my way out of is affiliated with a medical school and not an undergraduate school. Because of this, I have not had the displeasure of being a teachers assistant. However, graduate students (at least in my lab) train first year rotating graduate students (a.k.a. rotons) and during the summer, graduate students also train/mentor undergraduates and/or medical students. Since our lab studies a human pathogen, we typically get a decent amount of interest from both sectors.
Let me start with the medical students.
The summer before last my PI informed me that I would be in charge of the med. student. I was not happy about this arrangement at all, but I new my number was up and I couldn't avoid it. My anxiety arose from my observations of medical students that "worked" in our lab during the previous summers. The majority of them only bothered to show up for 2 hours per day, max. They all slept through the summer seminar series (I agree it is boring most of the time, but you can at least pretend that you are listening like the rest of us). They studied or looked at flash cards during lab meeting (again...pretend like you are paying attention). Finally, my favorite is the medical student who spent half his days making ice sculptures (using pellets from the departmental ice machine) and half his day trying to perfect his preservation of said sculptures. (I guess that qualifies as troubleshooting) Needless to say, I wasn't expecting too much from this guy.
To my surprise he turned out to be hard working, smart and listened (or at least pretended to listen) to seminars and lab meetings. I was so happy with him that I tried to work his data into a paper so that he could get an authorship out of the summer, but alas his data just didn't fit. He did win the poster competition that the medical students have at the end of the summer, so he got something out of it.
Now for the undergraduate summer student
I have mentored a few undergraduate researchers and quite simply, I HATE IT. Many of these students start the summer with only their basic sciences complete (ie. Biology, Chemistry, etc). Our lab primarily studies gene regulation, so we are heavy on the molecular genetics and molecular biology techniques.
My past summer students fall somewhere between OK and a nightmare from hell. The nightmare from hell refused to look anything up, refused to accept that he was responsible for the negative outcome of his experiments (and not negative in the negative data way, but in the your shit didn't work at all way) and to top it all off, he pouted all the time because I didn't spend every waking moment holding his chubby little hand.
I have no idea where my current student will fall. I am hoping she falls closer to the OK side of the spectrum. She did win a scholarship for this summer(I assume there was more than one applicant) and she worked in a lab last summer so she presumably has experience.
Currently we are at the stage where she is a time-sucking vortex.