I’ve completed much of the first book of BFSU (K-2) with my daughter several years ago. She’ll be in 6th grade next year and I’m wondering whether it would be better to do the 3-5 grade book or go ahead with the middle school age book.
The three volumes of BFSU are an unbroken continuum of lessons that build understanding in logical, systematic steps all the way from K to 8. Hence early lessons are prerequisite to later lessons. Therefore, I recommend actually doing a quick review of Volume I, since it was several years ago, then moving through Volume II before tacking Volume III. All lessons can be addressed in an age-appropriate manner.
I hope that others who have faced the same problem will comment as to what their experience has beed.