[bayjel]

I'd suggest a change of tack. Go for absolute accuracy in his answers, instead of just fluency. That is, every time he makes a mistake, you correct him and make him say the whole sentence again from the beginning, continually stopping and restarting every time he gets something wrong. This will concentrate his mind and make him really think about not only what he is saying but how he is saying it. He'll be constantly thinking and this make re-vitalize the lessons. Worth a try. Something different.