Parents are rebelling against the Common Core, even though its approach - fostering intuition through real-world examples - is the best way to teach math to kids. The real problem: No one has shown the teachers how to teach it.
This business of teaching is not nearly so easy as its master practictioners make it look! I know many, many teachers - including my own chemistry education students who are unable, with the best of intentions, to practice what they really would like to do. This New York Times Magazine article by Elizabeth Green describes the failure of New Math to revolutionize the teaching of the subject. It's not that we don't know how to do this - reform of math in Japan has been very successful, using methods learned in the US but seldome applied here. Common Core is just part of the most recent manifestation of math reform, and its success or failure depends almost entirely on whether those who determine how many resources are devoted to professional development of teachers, and also choose master teachers to train their peers. In the Common Core model, these decisions are made by agencies in each state, and I am not optimistic that they will find the courage to completely retrain virtually the entire current teaching cadre. Book publishers stand in the wings, ready to take on the task, but they are more likely to try to sell materials than to institute real change (that really doesn't need that many materials).