I suspect that what happens is the student start to think in a linear fashion, or just follows one pose on from the next. Thinking things like, "well now the character needs to lean over in this direction, and the hand needs to move over there so it can touch that, then the foot needs to go there and so on." There is even probably thinking along the lines of, "I think that would look better if the hips twist this way, or I'll move that hand over there so it read clearer," and so on. But this is no substitute for taking time out to consider the overall pose at a specific moment.
Good planning with lots of lateral thinking, thumbnailing and acting it out is a good start. But then I think people get lost in the process and the poses worked out while planning can become a vague memory or feeling in the back of your mind while animating. So I thought I would try to introduce a new word into your animating vocabulary, its something that I find useful for staying true to my original vision for a scene.
Its simply ENERGY.
I like to boil down my vision for a moment in a scene to a description of the energy in the pose. Is it a high energy moment? Is it the highest or lowest energy point or do i need to hold something back for another point in the scene? Is it positive or negative energy? What direction is that energy moving? Is the energy directed out at someone or something, or focused inwards?
Then when I start to work on the pose (no matter what the medium) I start to hunt for that energy level in that moment. I will work a pose over and over (what was that Frank mentioned in the coments from the previous post about animation being "sculpture"), always thinking back to that simple, easy to remember idea about how the energy will work in that pose. I know that I will also have to make the pose work in with the movement too, but always try to remind myself that I can't sacrifice the energy level to achieve that.
With me there is almost always not enough energy in my first stab at a pose, my natural tendency is towards a stiffer less energetic pose than what I initially visualized. So the question, "How can I get more out of this pose?" is a constant companion for me. It might be worth thinking objectively about your work in general and how you want it to improve it, keeping the energy of your poses (and consequently animation) in mind may be a good way of nudging you work in that direction.