See if he can find the pulse in a simple rock song in eights. Then try if he can stomp the bass drum pedal, and then hit the snare drum ( not necesssarily to a click or in time, but just play around a bit) - If it get's boring he will stop immediately, so it has to be fun, try new stuff everyday - but also play some of the stuff you did last time.
So for example, learn him how to hold the sticks in his hands - it doesn't have to be 100% correct the first time you practice with him. See if he can find the pulse in a rock song. Make him play the BD - snare beat... and that's bascially a lesson.
For the next lesson, you see if he can remember how to hold the sticks - then correct the mistakes a bit. Then you progress with a "harder" song, and then progress with the snare - BD beat aswell, to see if he can get the hi-hat with sometimes.
And so on - im no teacher - but that's what i would've done - but as you - I wouldn't know.