The age of the onset of menstruation, termed menarche, has been declining for decades worldwide. Approximately 12% of Australian girls reach menarche between eight to 11 years of age. Current health and physical education subject guidelines from the Australian Curriculum Assessment and Reporting Authority state that puberty education should be introduced to students between year levels five to six (ages 10-12) when many have already begun puberty. To explore how girls experiencing early menarche are currently supported in Australian primary schools, semi-structured telephone interviews were conducted with 15 primary school staff from separate schools, including teachers, principals, a school services officer, and a school counsellor. Thematic analysis identified three main themes, (1) the prevalence of deficit models of early menarche and children's capacity to know; (2) gendered gatekeeping of menstruation knowledge; and (3) systemic barriers and inconsistencies in menstruation education. Our analysis complements but extends recent calls for improvements to menstruation education in Australian schools. Affirmative menstrual support practices and facilities are needed in primary schools to normalise and encourage conversations with students about menarche and menstruation irrespective of age, gender, class or culture.