Sometimes formal sex education is taught as a full course as part of the curriculum in junior high school or high school. Other times it is only one unit within a more broad biology, health, home economics, or physical education class. Some schools offer no sex education, since it remains a controversial issue in several countries, particularly the United States (especially with regard to the age at which children should start receiving such education, the amount of detail that is revealed, including LGBT sex education, and topics dealing with human sexual behavior, e.g. safe sex practices, masturbation, premarital sex, and sexual ethics).