You might say that programs that encourage girls are "discriminatory" in some pedantic sense, but they don't keep boys from learning about math and science, nor

You might say that programs that encourage girls are "discriminatory" in some pedantic sense, but they don't keep boys from learning about math and science, nor do they discourage boys from going into STEM fields. The difference between this and actual sexism is that sexism discourages and systematically excludes people, typically girls/women, based on gender. Programs that target girls do nothing at all to discourage boys, because no one is saying, "These kinds of activities, careers, etc are only for girls now." Generally speaking, when any disadvantaged group gets together to discuss issues and take action on issues affecting them, they are not being racist, sexist, etc.