This task i.e. Grade Level Equivalents may be irrelevant because it should be noted that one of America`s most popular, early text books was The New England Primer.  Primer meaning the primary grades 1-3.  This home school and public school textbook series was used for 2 centuries between 1690 and 1890.  Some of the Primers were based on the 1611 King James Bible (British) and the latter, post Revolutionary Primers were based on the Americanized version of the King James Bible of 1769 as are today's "Authorized" KJV`s.  The point is that hands on parents using just two of the books below, say a Grade 3 and a Grade 8 book or an 8 and 12 set, could have suitable and alternate reading materials for the child for most of the public school experience.

It is recommended that the parents supply their own bound volume(s) containing "The Approved Authors of Excellence" in order to avoid any misunderstandings.  If several parents cooperate on the 1IntellectualFreedom.html letter, they can each declare their child's bound volume(s) independent of each other. Then the only parental agreement necessary would be on the other Approved Authors Addendum(s) and Grade Levels designations.