Coeducation is a way of running schools so that boys and girls learn together, in the same place and usually in the same classes. For a long time many schools kept the two apart; coeducation is the system that puts them in together. In a lot of countries that is now the ordinary pattern, so people often use the word when they talk about history, about policy, or about a school that still chooses to teach only one sex. It names the system as a whole, not one lesson. Though actually the idea in the word is simple: learning happens together, not in two separate tracks.