We know that women are underrepresented in math and science jobs. What we don’t know is why it happens.

There are various theories, and many of them focus on childhood. Parents and toy-makers discourage girls from studying math and science. So do their teachers. Girls lack role models in those fields, and grow up believing they wouldn’t do well in them.

All these factors surely play some role. A new study points to the influence of teachers’ unconscious biases, but it also highlights how powerful a little encouragement can be. Early educational experiences have a quantifiable effect on the math and science courses the students choose later, and eventually the jobs they get and the wages they earn.