Choose your TAs wisely

In one class that I've observed, the female student TA positioned herself near a couple of boys and spent the entire period chatting with them.  I would tell them to be quiet during the teacher's direct instruction (which took most of the period), but they rarely stopped talking for more than a minute.  (Perhaps the fact that I'm only here for a short time meant that I had no authority in her eyes.)  The TA informed me that she was in Running Start, so she goes to college in the morning before she comes to the high school, and then she works 20 hours/week after school.  It surprised me that someone with that much motivation would purposely disrupt the class.  I guess I saw it as disruptive, but maybe the TA didn't.  I don't know if teachers can choose their TAs, but if you can, make sure it's someone who will add to the class environment, rather than detract.