It is well documented that children who identify as a sexual minority or as gender-non-conforming are at an increased likelihood to experience adverse events and risk factors that can make it difficult to function in the community, home, and school environments. Lesbian, gay, bisexual, transgender, and questioning, intersex, or asexual (LGBTQIA+) youth report high levels of bullying and victimization with little or no effective intervention from teachers in schools. Research shows that not only are teachers ill-prepared to effectively intervene, but also they engage in homophobic behavior that contribute to a negative school climate. Previous literature shows that there is a lack of teacher preparation in teacher education programs to support this at-risk population. Therefore, teachers would benefit from ongoing professional development to provide knowledge, help them to challenge biases, and equip them with skills to best support LGBTQIA+ youth in schools. There is a lack of empirical studies that show the effectiveness of teacher professional development on LGBTQIA+ issues. This study was conducted to add to the literature regarding the effectiveness of teacher professional development on increasing teacher knowledge, attitudes, and skills in order to support LGBTQIA+ youth in schools. The two-hour professional development model utilized social learning theory as a foundation for facilitating teacher learning. Utilizing a quasi-experimental approach, this study provides preliminary evidence for the effectiveness of teacher professional development in increasing knowledge, challenging attitudes, and equipping them with skills. The results of the study also show that teacher professional development is able to lower self-perceived levels of homophobia. However, there was no relationships between participants' self-reported knowledge, attitudes and skills regarding supporting LGBTQIA+ youth and these participants' homophobic beliefs. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]