Adolescent girls commonly show a reduction in school participation due to 1 menstruation-related teasing and anxieties. Menstrual hygiene research and policies 2 almost exclusively focus on girls and women, leading to a lack of knowledge on male 3 attitudes toward the topic. We conducted the first quantitative survey of period teasing 4 in schools in sub-Saharan Africa. We surveyed 432 adolescent boys and 524 girls in four 5 co-educational secondary schools in Western Tanzania. Thirteen percent of girls 6 reported experiencing period teasing, and 80 percent fear being teased by male peers. 7 Four out of five girls fear teasing related to insufficient menstrual hygiene 8 management—leading to lower school attendance, and difficulty concentrating and 9 participating in the classroom during their periods. Boys reported engaging in period 10 teasing because periods are embarrassing and when girls smell or have blood stains. 11 Despite this, boys are well-informed about the basic biological facts of menstruation. 12 They scored 60 percent, on average, on a menstruation quiz and have received 13 information from the school curricula and health workers. However, boys expressed that 14 girls should hide their periods and not discuss it with male peers, male teachers or 15 fathers. Period shaming and teasing are prevalent in secondary schools, with serious 16 implications for schooling access. Lack of suitable menstrual hygiene practices causes 17 social harm to girls through commonly-practiced teasing. Including male students in 18 menstrual health education is important to reduce acceptability of teasing behavior 19 related to …