He's just going to talk really late, that's all there is to it. You can lead a horse to water, but not make him drink - you can put a toddler in his bed, but not make him sleep - and you can say "ball! ball! buh-buh ball!" 'til the cows come home, and if he's not in a "b" mood, buh-buh-buh will never happen. He knows what a ball is, he likes them very much, throwing and fetching, but he absolutely will not say buh on command. I'm beginning to think he doesn't see the point. He KNOWS the colorful sphere is a ball - why bother to SAY it? The same for kitty, doggie, all that. What silly grownups we are, that we want HIM to tell us what a ball is and what a kitty is.
Our "home assignment" - business as usual!