Recognizing a need for consistent learning goals across all states, the Common Core State Standards (CCSS) began to be developed in 2009 as a state-led effort to coordinate math and English academic standards. By providing educators with a clear and consistent framework to determine student proficiency, the aim of the Common Core is to ensure that all students graduate high school with the knowledge they need to succeed.

Although controversy has followed the development of the Common Core from the start, in recent months the debate has become much more heated, with some states opting out of the standards altogether. There are, however, currently 43 states, the District of Columbia, and four territories that have voluntarily adopted and are moving forward with the Common Core.

Follow the timeline below for details on the evolution of the Common Core – from development, to adoption, to, more recently, the lawsuits that have been filed in opposition to the standards – to help understand this now polarizing issue.