This is a great blog post by Tim Shanahan on the role of a research-based Scope and Sequence in teaching phonics. We know from research that children with Down syndrome benefit from structured, systematic approaches to teaching in general. I have found this to be particularly true when it comes to reading instruction.
openbooksopendoors.com 
I want to read the blog post, but the link didn’t work ; (
Hi Crista–thanks for letting me know about the broken link. I’ve updated it.