The Gay, Lesbian and Straight Education Network (GLSEN) National School Climate Survey is our flagship report on the school experiences of LGBTQ youth in schools, including the extent of the challenges that they face at school and the school-based resources that support LGBTQ students' well-being. The survey has consistently indicated that specific school-based supports are related to a safer and more inclusive school climate, including: supportive educators, LGBTQ-inclusive curriculum, inclusive and supportive policies, and supportive student clubs, such as Gay-Straight Alliances or Gender and Sexuality Alliances (GSAs). The full GLSEN 2019 National School Climate Survey report includes information on LGBTQ middle and high school students' experiences, including: (1) Hearing biased language, from both students and educators; (2) Experiences of harassment and assault; (3) Anti-LGBTQ discrimination; (4) Effects of a hostile school climate on educational outcomes and psychological well-being; and (5) The availability and utility of supportive school resources. This report also examines demographic and school differences in students' experiences, and explores LGBTQ students' experiences with GSAs. In addition, this installment of GLSEN's National School Climate Survey also includes an extensive exploration of how school climate has changed since we began conducting this survey, including insights into how racist remarks and harassment, feelings of safety regarding citizenship, gender-based discrimination, and LGBTQ student identities have all changed over time. [For the 2019 executive summary, see ED608535. For "The 2017 National School Climate Survey: The Experiences of Lesbian, Gay, Bisexual, Transgender, and Queer Youth in Our Nation's Schools", see ED590243.]