Oh gosh Irena - I wouldn't hold him back! I don't have any research or articles to offer up to show your dh, but I do have a life-time of experience as a very very short person. My dh was also really short up until he hit high school, then he had a huge growth spurt, and the same thing seems to be happening with my ds, who was always the shortest *kid* in his class (note - not the shortest *boy*, the shortest *kid*) up until last year, and now he's having a large growth spurt. He's also always been one of the oldest kids in his classes, because we live in a district where parents *don't* redshirt and his birthday just missed the kindy cutoff.
I mention our heights because - had we held ds back another year hoping that he wouldn't have been the shortest kid in class.. he would still have been the shortest kid in class! And as a short person myself, I can promise you it's a lot easier to deal with a little bit of height disadvantage in school than it is to sit bored to tears because you are older and farther along developmentally than the school curriculum is set up for.
Your older ds is also needing subject acceleration in school, so I wouldn't be surprised if your younger ds does to - at his appropriate age/grade level. Definitely not worth risking holding him back another year.
The other thing about height - my older dd was always one of the tallest kids in her class.... up until she hit puberty. Now suddenly she's not so tall.... in fact, she's not quite as tall as me at this point, and according to her ped, she's about to hit that age at which girls stop growing. No *way* when she was younger would anyone have ever thought she'd be "short". Yet, she's my child that I often wished I *had* held back in school due to emotional maturity. Still wonder about it!
So as you can see... I am very against making school-grade decisions based on physical stature

polarbear