I think some of it may have to do with funding and test secrecy. Our state tests include many essay questions in Reading and in Math (full step by step explanations/mathematical oroofs) starting with the 3rd grade assessments. This in turn requires the hiring of special personnel to grade the essays.
Interestingly, because DS7 was subjected accelerated to the 3rd grade GT math class, he is required to take the 3rd grade state math assessment with the other 3rd graders this year. However, even though his 3rd grade GT math curriculum covers fourth grade math, they are not assigned the 4th grade assessment.