The Common Core curriculum-content standards are a national listing of topics that students are expected to learn in the subjects of English and mathematics. An independent initiative of three Washington, D.C.-based organizations created the national standards, but they were endorsed and promoted by the Obama-era U.S. Department of Education. The standards were released in June 2010. Their summer launch meant that teachers and parents did not have much of an opportunity to discuss their merits and drawbacks. Abiding by the standards was necessary for states to be eligible for massive federal grants. California adopted the national standards and fully implemented them in 2014-2015.
This was a mistake. Looking at how the states students performed in math before and after the standards were implemented, its clear that the old system served students much better. Before Common Core, California had its own mathematics curriculum-content standards. They had been written largely by the faculty of the Mathematics Department at Stanford University and were adopted by the state in December 1997.