They feel they are loosing control of what their children are learning and not learning.
Check it out:

More parents are removing their children from traditional school environments and are choosing to homeschool them instead due to increased concern over the use of the Common Core standards.

The Heartlander reported earlier this month that in the state of North Carolina homeschooling increased by 14 percent during the last academic year as the controversial Common Core standards grew to be more of a concern for parents.

Similarly, a new report at Fox News indicates that the number of students homeschooled in Virginia, California, and New York has increased.