Much of the criticism focuses on the sheer number of tests now being applied in public schools: From pre-kindergarten through grade 12, students take an average of 113 standardized tests, according to a survey by the Council of the Great City Schools, which represents large urban districts.

Of these, only 17 are mandated by the federal government, but the backlash that began when No Child Left Behind started to hold teachers, schools and districts strictly accountable for their students' progress has only grown stronger since "Common Core" gave the criticism a common rallying cry.

"There is a widespread sentiment among parents, students, teachers, administrators and local elected officials that enough is enough, that government mandated testing has taken over our schools," Schaeffer said.

Teachers now devote 30 percent of their work time on testing-related tasks, including preparing students, proctoring, and reviewing the results of standardized tests, the National Education Association says.

The pressure to improve results year after year can be demoralizing and even criminalizing, say critics who point to the Atlanta test-cheating scandal, which led to the convictions 35 educators charged with altering exams to boost scores.