Educational professionals sought to reform schools by:

a. refusing to place children who could not keep up with their peers in special classes.

b. requiring all teachers to hold graduate degrees.

c. reducing the role of school boards.

d. having voters elect superintendents to increase accountability.

I believe the answer is: making school boards non-partisan

Partisan school board would most likely make the materials in the curriculum to be leaning toward a certain political affiliation.

For example, if the school boards is controlled by members with Republican-leaning, the material of economic subject would be focused on the benefit of low taxation for the economy.