I think this quote is more of an hyperbole, however the principle of the quote would be: spend most of your energies on the most difficult students, not on the

I think this quote is more of an hyperbole, however the principle of the quote would be: spend most of your energies on the most difficult students, not on the gifted ones; probably the most gifted student will find something to satiate their interests anyway and their families are already providing them tangentially with learning material. An educator I know likes to say that's not the really worst students you should spend your energies on, but the ones just a little better, that's where the best return on investment is, according to him.