I could write many posts about mistakes we made whilst homeschooling, but I do know of one thing we did that was correct. When we had to decide grade placement for our children, we followed the public school's snapshot date for school entry. We did this with purpose for several reasons. One, we knew from our backgrounds in education that those dates are not determined in a random manner. They are based on research and experience. Two, we had our own personal experience with seeing patterns of "early birthdays" and "late birthdays" in relation to performance and readiness in our classrooms. Three, and our foremost practical reason: we knew that anything could happen. What if one of us was in a horrible accident, or worse, died? An even worse scenario: what if one of our children were seriously ill and required hospital stays or lengthy treatments? We would not be able to continue homeschooling in those circumstances and we would need to enroll them in school, even if it were a temporary arrangement. The schools wouldn't care as to which grade we thought our children belonged. They would still (or should if the registrar does his/her job correctly) base enrollment on their birthdate. Why risk confusion or even humiliation if they were "knocked down" a grade?
A child's grade label need not limit them in terms of their homeschooling experience. Enrichment--in any circumstance--is best when done horizontally, not vertically. In the United States, we are guilty of seeing advancement in terms of pushing through to the next topic or level. Instead, we should encourage further exploration and development of the topics at that grade level, especially in the elementary years. Your child knows all of his math facts? Great! Now, see if he understands the various properties of those facts. Can he use them in an algebraic manner? Can he use them in multi-step word problems and open-ended problems? Your child knows how to spell his spelling words? Well done! Now she can focus on using them in their correct context whilst constructing sentences, paragraphs, and complete compositions. Your child knows EVERYTHING about the solar system, huh? Well, that's just...impossible.
It's probably not the lone correct move in our homeschooling journey, but I think it was certainly our best. Rules aren't always there to inhibit. Sometimes they are there for the best results from the greatest number of people.