That is a direct quote from the California Department of Education’s draft framework for K–12 education. Robby Soave has much more on the framework here; it argues against separating kids by ability before high school and downplays the importance of giving bright kids access to high-school calculus.
You can argue about when schools should start providing different classes for kids with different skill levels, and about whether smart seniors should be focusing on calculus or some other topic. But when the “experts” in charge of your education system can’t even admit that giftedness exists, and they insist on holding advanced kids back in the name of “equity,” you just might have a problem.
Incidentally, not all leftists are this stupid in the face of human differences. You can read my review of Fredrik deBoer’s The Cult of Smart here.