Solfege: the system of ear-training that names the steps of the scale with the syllables do, re, mi etc. I find it very useful in singing, not very useful in instrument playing.
First of all, what is the goal? Is he expected to be able to conduct and sing solfege at school?
Whatever the reason for learning, start simply: have him sing and clap the beat, or just move his arm up and down to the beats, not worrying about conducting in 3 or 4. Make sure he can feel the beat at all before expecting him to find the downbeat!
Then help him feel what I call the "strong beat", either by increasing the strenghth of the clap or the arm movement, or by changing the motion, for example CLAP pat pat CLAP pat pat (for 3/4 time).
That may take some time, but when he really gets it, he's ready to try actual conducting motions.
Good luck! I recently heard of a survey that said that over 75% of US high school seniors could not walk to a steady beat. Getting their bodies to conform to the music isn't as easy as we musician-types think it is!