I've been told the same thing at my DS8's school for the last year and a half. (He's in 2nd grade now.) If I hear "we want him to go deeper, not wider" one more time, I might just scream!
My kid doesn't need to go any deeper with understanding what 7+0 is! Sorry, got on my soap box there...
What I finally realized is that my DS really doesn't need more extensions. He needs to learn more. That's what his brain can handle and what he needs to stay motivated. So my advice would be to advocate for opportunities for your child to "prove" that he/she knows and understands the material, so that he/she can move on. I sure wish I had done that for my DS...
