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(CNN)Black history is American history.

It’s easy to say. But while most grade school teachers agree that the experience and contributions of African-Americans are essential to understanding the nation’s past, only about 9% of total class time — about one or two lessons — gets devoted to it, a 2015 study by the National Council for the Social Studies found.

Part of why, the study found, is that teachers often lack the confidence to teach black history and aren’t sure “how and what content should be delivered.”

Certainly worthy are these trailblazers, who excelled in fields that, until they made their mark, had been off-limits to black women.