Well the WT scales can be taught without the key colour being changed. One WT scale is the 3 back keys plus 3 white (CDE). The other is the 2 black keys plus 4 white (FGAB). So you test them in playing the 3-3 wholetone scale and the 2-4 wholetone scale. You point out what we mean by wholetones, specially showing where they cross from black to white. You also point out what we mean by semitones. Point out that if you move by a semitone, you get into the other WT scale. For kids who have a logical, mathematical or scientific type of brain, this would appeal. For kids without (aaggghhh), you just teach the mnemonics without trying to explain anything!
I always wanted explanations when I was young, and was never satisfied with the conventional answers. Why is treble clef different to bass clef? The fact is, it was a quirky error of judgement somewhere in history! There is no logical reason why they could not have gone with the French violin clef that had the G on the bottom line.
When I first saw that ABCDEFG made a symmetrical pattern, i thought "So thats why the notes are named the way they are!" If we were meant to start with C, it would have been called A!
I dont teach kids to pass theory exams any more. I try to teach them piano skills, one of which is playing sheet music, classical style. But too often, the kids aim is to do other things and I try to keep a balance. Sometimes we play melody by solfa and "Home" (tonic) and "Away" (dominant 7th) chords, or we interpret chord symbols and make our own arrangements or versions of pieces. Also kids want help with how to pick up pop songs by ear, or how do some improvising in boogie blues style etc ...
Playing classical music is not what most would people want to do, unless it was a bit easier.
Anyway thats my outlook ...