A good teaching assistant has to be motivated. They have to be engaged. They need to bring their A game.
Unfortunately, there are teaching assistants who are not motivated and who do the minimum possible, sometimes without a care about quality or accountability.
In extreme cases, there is nothing you can do. We have been there. We end up doing what the TA was supposed to do. We never want to see the TA again. This note is not about these TAs. This note is about the TAs who need a little bit of help, can enter the recovery program and come out the other side a good, perhaps great TA.
The lack of motivation might be seen in different ways. Executive functions which are misfiring can be clues (planning, execution, timeliness, paying attention to details, paying attention to requests). General responsiveness in communication can also be a clue. Taking shortcuts, purposely (or not) creating situations where others have to do their work. The type and degree of care being given the students they are supposed to be helping. There are many ways that the lack of motivation can impact the class. An unmotivated TA will not be proactive, be a participant. They will be waiting for instructions, what to do when, how to do it. They will not be helping to create a good class, a better class. They will not be looking for ways to improve the class.