It is important to encourage both "visible students" and "invisible students" to establish self-confidence and to live naturally, being themselves. It is also important to help students grow as humane adults who can accept diversity, respect each other, and support minorities. This article presents a lesson plan that aims to help students learn the difference of sex in human beings and in animals. It also aims to help students learn the existence of sexual minorities and understand them properly. (Contains 6 notes.)