Contraception methods will be added to the 11th-grade health curriculum at Marshfield High School next school year, a change approved June 18 by the School Committee. The existing curriculum includes information on reproduction, preventing sexually transmitted diseases, and the benefits of abstinence, but not other methods of contraception. Parents will have the opportunity to excuse their children from the lesson, which will last about 20 minutes and include information on abstinence, spermicide, diaphragms, intrauterine devices, male condoms, “morning after” pills, and birth control pills, according to Ellen Martin, assistant superintendent of schools. State guidelines have called for pregnancy prevention to be included in high school curricula since at least 1999, and Marshfield was one of few area schools not teaching a similar lesson, she said. Marti Morrison, chairwoman of the School Committee, said the change passed without controversy among committee members or the public.