If it's a day where we need and should get work done and they haven't any logical reasons for not "wanting" to, then I will say, "tough part of life is realizing you have to do things that need to be done when you don't want to", and then we'll work on school that day.
Sweetie, there are so many things that some days I just don't want to do. I hate making my meal plans some weeks. When the temps drop below zero, I don't want to go to the barn and take care of the goats. But, to get where we want to be in this life, we have to take steps every single day on that journey. Right now your journey is a journey of learning. So we are going to take those steps together today. You can do this.
If they really look and act like they need a break then I let them have it. If they don't look to overwhelemed and are acting ok, then I push them into the day. I try to schedule a day "off" once a month. This way we all get a day to recharge that isn't a weekend.
I remind them that their job is school. It is a responsibility that they have and it is really important. I also remind them of all the things that I don't want to do on a regular basis, but have to because I am "Mom".