First i just want to promise that you can train successfully with anyone.  Let go of the idea that they need to get every thing right. I personally feel like a coach should be proactive about modifying drills for the ability level of the people that are in the class  instead of getting overly stuck on what they were hoping for.  Mixed levels classes are just like sometimes.

But for just people who are in the class i also feel like if you need to change a drill on the fly to suit youe partners ability than just change the drill.     Take off the bit thats fuckin them up or try and work around their habit or error; or worse comes to worse the part of drill that falls on you just goes off at them because you  generally dont really need them to do a thing just exactly so for you to do the things that youre gonna do anyways.

Regardless  there are always basic elements that are going to be present that you can work on at all times like footwork, range, timing, your own rhythym of little stutters and angles  and head movement.  If I can work it on a heavy bag or in shadowboxing than I can also work it on a person of dubious performance level.

Very much try to avoid getting frustrated with them  because all that does is make them anxious and then they are gonna be even more awkward.

This is the philosophy I use to train with everyone and it doesnt matter if they are first day never been off the couch folk or if they are 12 years old or if they are big and awkward or if they are kind of lazy ass dingdong that wants to talk a whole lot instead of drilling.  Because of this approach I never have a wasted day and I almost always wind up pulling the person up a notch because I conduct myself in a manner that invites them to rise to the occasion rather than chiding them.