Don't tell them that its to a certain std. Just tell them this is how you are required to fly to get your licence. Teach a CPL std to your student who's doing his PPL and he will pass the first time. It does not mean you have keep the pressure on, just pick them up when they forget to put their hand on the throttle, after a while they will do it instinctively. It takes time but you will develop the right habit. If that doesn't work wack em on the hand with the dipstick as my instructor used to do! better yet tie a lanyard lose around their hand then around the throttle, that works too! Goodluck.