Don't teach him a chord melody song, teach him how to make it.
It would be the same problem with teachers who promise to teach kids songs, but the kids don't "know" how to play them, they just play them because they know it goes that way.
It will be way more valuable for him to teach him how to arrange his own chord solo and let him show you what he's working on, then give him small suggestions.
A great song to start with is All The Things You Are. If you teach him basic root position 7th chords, that will be enough for him to arrange his first CM, then you can start teaching him how to build his own voicings based on the melody or the chord he wants. This includes reharmonizing, restructurizing chords, and other techniques such as parallelism, walking basslines, ect.
This way, he'll be able to learn how to play the chord solo in more than one way, and then put it all together in one, so there's a lot of variety and it comes out great, he'll also start school with a great idea of how to do this, and he won't be the worst student there
