Background: There is a gap in the literature regarding data on sexting among youth under the age of 16 whereas the problems related to this practice could affect them more because of their ongoing development. This study aims to determine the prevalence rate and characteristics of sending one's own sexually related image among middle-school teens. Methods: Data were obtained from a web-based in-school survey conducted between October 2019 and February 2020. The sample comprised 3006 (mean age 13.7; 50.2% males) 10th-grade pupils in the canton of Vaud (Switzerland). Participants were asked "Have you ever sent a sexually related/sexy image of yourself?". Analysis of variance/chi-square tests and multinomial regression analyses were used to compare the groups. Results: Overall, 93.0% reported never, 3.7% once and 3.3% several times. No gender differences were found. Sending was associated with older age, low academic performance, cyberbullying victimization and reception of unsolicited sexually related images. Conclusions: Education and health professionals should be aware that it is necessary to discuss the theme, perhaps with a more global approach including pressure, consent, exchange of nonsexual images, and so on from an early age. The context and reasons for sending remain to be explored, particularly to determine if the pressure is greater at this age.