This is going to be short and to the point: Don't make training a threat in relationship to punishment.
I have heard, and have used this phrase myself, "I'll just make him/her train all day." This in response to a firefighter that is a problem. Negative attitudes, lack of interest, or any other behavior can be attempted to be changed by making them train, but in wont work. It will only make them hate training all that much more.
As an officer we need to motivate our people to be the best they can be. Making them train as in "you will straighten up or you'll train more" is a loser. It doesn't change the behavior and they will not be engaged in the training for the right reasons. Then they don't grasp concepts and techniques because they are there physically but not mentally,
If you want to give them busy work, give them busy work. Training should be used to enhance skills, enforce or enable mastery, learn new skills and to become more proficient at our job. It should also promote crew cohesiveness and team work. That is hard to accomplish when we use training as punishment.
Make sure you know the difference and that you use each appropriately. Make training a reward, make it a positive time at the firehouse. Let the trouble makers do some inventory, do a little extra cleaning or anything but making them train. Just don't use training as your crutch to change an trouble employee.