Re: One student who doesn't understand
Have you ever seen an anatomy text? The ones with clear plastic pages with a given anatomical system on each so that the body is built up one "layer" at a time?
Some people...like me...can't learn holistically. That is, we can't learn it all at once. We have to break it down into parts/layers/etc. then reassemble it one layer at a time.
Have the student perform a simple technique as solo kata. He'll have to do it enough times so that the outer form of the technique has soaked in but not enough to get super bored. Start him out doing it step-by-step with pauses at critical points. The pauses need to be long enough for him to reflect on his form/body/position and that of his imaginary uke. We 2 seconds. Only when he has it down should he go on to do it fluidly.
Then give him an uke. But...and this is important...the uke is *good* at his job and his helping nage with the form of the technique vice giving him any resistence. Repeat the process of doing it step-by-step with pauses first then graduating to slow, fluid movement.
That's a lot to do for a student that is in class. You might consider breaking the class into groups that are doing things in different ways with this student in a group that is doing it the way I mention.
You could take the more senior students off and do randori with them and have the person cycling out of the randori go to the other group to be leader/good uke.
Hope that helps,