Background Endometriosis is a long-lasting state in which endometrial-like tissue is found outside the uterus often on the reproductive organs, bowel, and bladder. Aim To evaluate the effect of educational intervention and referral for early detection of endometriosis among technical secondary school students. Patients and methods A quasi-experimental research design was used to achieve the aim of the study. Setting The study was carried out at technical secondary schools for girl students at Minia City. Sampling A total of 300 adolescent girls were selected using a cluster sampling technique. Tools Four tools were used for data collection: tool 1, sociodemographic data and menstrual history; tool 2, symptoms/risk factors assessment tool for early detection of endometriosis; tool 3, knowledge assessment tool about endometriosis; and tool 4, management practices assessment tool. Results The current study revealed that 72.8% of girl students had poor knowledge about endometriosis in pretest, which decreased to 20.3% in posttest. In addition, there were statistically significant improvements among referred girls regarding their management practices related to symptoms suggesting endometriosis in pretest (10.3%) and posttest (77.3%). Furthermore, there were positive correlations between knowledge about endometriosis among studied students and their symptom management practices after implementation of the educational intervention. Conclusion Implementation of educational intervention among adolescent girls was effective in early detection and early management of endometriosis and in improving their knowledge and their management practices regarding endometriosis. Recommendations More research studies are needed to increase adolescent girls’ awareness regarding endometriosis because there are scant research studies in this field.