Autonomy is often discussed as a necessary condition for professionalism in any field, including the teaching profession. In the educational context, autonomy is seen to be critical for teachers to be able to synthesize their knowledge and skills and translate them into effective classroom practices in the best interest of their students. In response to national and global trends primarily associated with neoliberal reforms and their constraining consequences for teacher autonomy, researchers have been trying to unpack this concept and demonstrate evidence on how it affects teachers, students, and the educational system in general. However, this empirical evidence is both quite scarce and controversial. In this dissertation, I define teacher autonomy as a decision-making space created through the freedom from input and output control and identify four types of autonomy: limited, moderate output-driven, moderate input-driven, and extended. Using the data from 43 countries from the Progress in International Reading Literacy Study (PIRLS) 2016 database, I explore the moderating role of each type of autonomy for classroom practices, student achievement, and educational equity. I find that although students in countries with moderate input-driven and extended autonomy have the highest achievement compared to limited and moderate output-driven ones, their teachers, overall, use key classroom practices less frequently, as well as the effectiveness of those practices is relatively low. Findings are more consistent in relation to educational equity. These two groups of countries experience the lowest achievement gap in reading, as well as have teachers who use effective strategies with more frequency with disadvantaged students. In addition, classroom practices in countries with extended teacher autonomy and, to a certain extent, with moderate input-driven one show more potential to contribute to narrowing the achievement gap. [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/en-US/products/dissertations/individuals.shtml.]