In the early years, how big of a deal is it to be working a grade-level or two grade-levels ahead?

For example, when I look at a kindergarten workbook and a first-grade workbook, I don't notice a huge difference. And of course as an adult, it all looks easy. And I'm also a gifted adult, so trying to think back to what I knew when I was that age isn't an appropriate comparison either.

The main reason I'm asking is that I'm currently homeschooling DS5. Husband is not fully on board going forward and would like to enroll him in school next year. There's a part of me thinking that if I have DS complete a first grade workbook, it will be a sort of "proof" to hubby that he really is ahead. Though we have test results showing giftedness, DS isn't really the overachieving type, so I think it's hard for hubby to gain some perspective.

He's not yet reading, and I'm suspecting dyslexia (which is a whole different beast), but now thinking this, I'm starting to adjust my approach to reading with him. He also hasn't memorized the math facts, but he understands what's going on. But beyond these, I think his skills are a bit more advanced and that sending him to school would be a disaster.

So, I guess what I'm asking is if at this age, "working above grade level" really is significant.