I've never seen meditation or anything like it in the place where I train, but I'd like to share my thoughts, anyway:
Once taekwondo is regarded as a way of constructing and conducting one's self (or something like that) more than just a fighting system (despite the fact that it also includes this part), I believe that meditation is something welcome to the classes. I believe it could be useful even to people more focused in fighting, sport or self-defense, but it seems to be particularly useful in a "do" perspective.
Actually, I'm not strictly talking about meditation, but putting aside a time (that doesn't need to happen always) for reflection, concentration and relaxation amid martial art classes. This time could be useful to help students become more relaxed and prepared to work with their bodies, correct their breathing, forget about issues from outside and stay motivated and open for learning -- and, off course, reflect about what is being learned and how to improve. Is this strictly meditation? I don't think so, but I think it is a nice beginning that can later invite some practitioners to meditate where it seems to work better -- when the person feels it is needed.
To me this seems particularly important in kids and teenagers classes, as the younger people need some help to stay focused and at the same time relaxed.
It is good to remember that even if meditation doesn't work exactly as it should be with most people, the "peace time" can be very useful to most, and there are certainly some people that don't even have such kind of opportunity in any other time of the day, or haven't even been ever teached about the utility of stopping the everyday rush just for a while. Maybe later they would use the method also outside, but first they would need someone to show them about it. So, as I said, if taekwondo is "do", and goes beyond the classes and into everyday life, it looks like a good idea to have meditation time in classes.