Growing opposition to the Common Core academic standards for the nation’s public schools is threatening to slow down and derail the initiative.

Forty-five states and the District of Columbia voluntarily adopted at least some of the Common Core State Standards Initiative, a state-led effort to establish a single set of educational standards for language arts and math in grades K-12. Slated to start next year, it would replace standards created by each state that Common Core advocates say are not adequately preparing students for life after high school.