How are his knitting skills otherwise? If he's knitting well flat, I'm not sure why he couldn't learn to knit in the round (although I've never personally done magic loop).
Also, are you planning to stay with him during the class? Maybe they're worried he won't be able to sit through the class, will become bored, etc?
If the class is hosted in your lys, how about bringing him in w/some examples of his knitting to "prove" that he is ready and willing to learn magic loop?
Knitting homeschooling mom to 3 kidlets
Bayerische Socks by Eunny Jang in Knit Picks Risata (for ME!)
in queue: Swirl glittens; lacy raglan for me; new cabled sweater for dh