Something is to said about the highly successful school systems that educated our ancestors through the founding of our country.  Most adults in the present day would struggle to pass a standard Grade 8 test from the turn of the century:
https://newrepublic.com/article/79470/1895-8th-grade-final-exam-i-couldnt-pass-it-could-you

The Spaulding Schools seeks to build from what has always been tried an true: Manageable class sizes with multiple grades in every room.  Why is the important?
Well the manageable class sizes need not further explanation; as most of us know (and is often said) that the best way to learn something is to do it though teaching another.  Instead of having an environment as the present public systems do, where grade ones only mingle with grade ones and grade twos learn with grade twos and grade threes pick on the grade ones (tongue planted firmly in cheaque).  The Spaulding Method and subsequent Spaulidng Schools create an atmosphere where the grade threes can facilitate the learning of the grade twos and the grade twos facilitate the learning of the grade ones.  Each grade affirming knowledge of their material as the class mates facilaite one another. 
This environment also enables a student in grade two (for example) to be operating at a grade three level in math while still finalizing their knowledge an understanding of grade one material.  Each student at the end of the year will pass their given grade level for their age while preparing for the next level in the coming year.
Many students actually feel great pride when they realize that they are operating above their grade because of a resulting “knack” of learning material.  That confidence then translates into other areas of their learning and life.