One of the things I love about homeschooling our children is that we can go at our own pace.
If a 4th grader needs extra practice with basic spelling skills that other kids her age have already mastered, (and she does) we spend all the time we need on it. No special testing, special diagnoses, or special classes. We implement tactile spelling practice with shaving cream , do extra practice with basic words, prefixes, and suffixes, and allow for growth at her own pace without pressuring her to keep up with the rest of the class.
Conversely, if a child is soaring ahead of her "grade level", we don't feel constrained to keep a slow and steady pace if it is unnecessary.
The below video is a good example of allowing children to go at their own pace. My kindergartener came to me recently to excitedly tell me that she knew how many kitten bits "Birdie"  eats in a day if Madison  feeds her 12 pellets, 6 times each day.
I was stunned when she explained to me how she figured it out! She demonstrates below. (Email readers may need to click through to see the video.)
When I taught in the public schools , each year I would have very precocious students who could have gone far ahead of the rest of the class, but there was no possible way I could tailor a schedule and curriculum for each student in my class. I spent much of each day conducting crowd control anyway, which involved keeping students in their seats and quiet, so there just wasn't much time for exploration or independent interests.
With homeschooling, we can skip ahead or lag behind if needed, to suit the child's needs. With one of my children, I completely skipped first grade math and started her formal schooling with a second grade math book. I remember someone telling me, "You can't just skip grades like that!", and if you've been reading here long, you probably know that, of course, I didn't listen.
I knew she, like Reagan in the video, had a firm grasp on basic math skills and did not need useless repetition in those skills.
Homeschooling allows each child to proceed at his or her own pace in each subject.
Zooming ahead in reading and lagging behind in math? No problem. Remedial spelling and above grade level math? Got it covered.
Let your child's abilities, not the curriculum, tell you how to proceed.