Background: Transmission of sexually transmitted diseases (STIs) in the United States continues to rise, and in 2018 the incidence of syphilis, gonorrhea, and chlamydia increased for the fifth straight year. While teenagers endorse being less sexually active than prior generations, rates of STI transmission among adolescents continues to increase, especially in populations with limited access to care. One reason cited for the increasing rates of transmission among adolescents is their inability to undergo confidential testing. School-based clinics can bridge this gap by providing reproductive services that are easily accessible to students. In early 2018 a university-affiliated school-based health center partnered with the local health department as an official HIV and STI testing site to provide free and confidential testing to students in three underserved high schools. We sought out to examine the rates of four sexually-transmitted infections among our adolescent high school patients. Methods: Retrospective chart review of individual STI results from August 2018 to March 2020 was completed. During their school clinic visits, patients were tested on a voluntary basis for HIV, syphilis, gonorrhea, and chlamydia as determined by risk factors for disease transmission and willingness to undergo free and confidential testing. Results: A total of 485 individual high school students (59% Females, 41% males) underwent STI testing. Two thousand twenty-three tests were performed during the study period (HIV: 504, Chlamydia: 605, Syphilis: 488, Gonorrhea: 605, and Hepatitis C: 1). There was no gender difference in the rates of Chlamydia (15.6% for males vs. 15.5% for females). Only a few adolescents tested positive for Gonorrhea (5/605), syphilis (2/488), or HIV (1/504) in the same time frame. Conclusions: (1) Chlamydia is, by far, the most common STI among high school students in these local schools. (2) Forming a relationship with a local health department provides an effective means of administering HIV and STI screening in low-income settings to at-risk adolescents. (3) A school-based healthcare center is a suitable and effective location for confidential HIV screening and STI testing. (4) Despite abstinence-only education, there is a large unmet need for sexual and reproductive health services among high school students. Future Directions: (1) Further evaluation of the perceptions of sexual and reproductive health topics among adolescents in low-income settings. (2) Investigation into the drivers of transmission in the local community. (3) Implementation of unbiased comprehensive sexual and reproductive health education. (4) Advocacy for higher levels of access to confidential and comprehensive reproductive health services for adolescents.