I use All About Spelling. I have no idea whether it is CM friendly, but I love it. My own boys are not behind, but I am a certified teacher/tutor, also. I use the same curriculum with my tutor students who are VERY behind! The main reasons I like it is because it is very step-by-step, there is lots and lots of review of the spelling rules, and it does not have a grade level. You start with level one. When your child has mastered every concept in level one, then you move on to level two, and so forth. I highly recommend starting with level one. (Although, you can order each level independent.) The materials in level two build on the skills in level one. I think it would be confusing to start on level 2. I usually start my students on level one. They fly through it and then we move to level 2. My students have done great with it. It is very versatile and can be used with lots of ages. I have used it with a 6yo, 7 yo, 11 yo, and 16 yo. (some mine, some my tutor kids) I have even teased my hubby that I am going to start teaching him some spelling with it! 🙂 There are reviews all over the internet if you want to investigate it.
Jennifer