If someone is discriminating, they can judge what is of good quality and what is not, and they choose with care. A discriminating reader notices lazy writing. A discriminating ear hears the difference between a fine singer and a loud one. In this sense it is a compliment: you have taste, not a wide-open mouth for whatever is in front of you. You will meet it in reviews, museums, and food writing more than in the playground. Though actually, this is the trap. Discriminating looks like discriminatory, and many students think both mean “unfair.” Discriminatory is the unfair-treatment word. This one is closer to “having a sharp eye.” The verb discriminate can go either way — “tell things apart” or “treat people unfairly” — which is why the -ing adjective still makes people nervous.