The past several years have presented the astronomy education research community with a host of foundational research dissertations in the teaching and learning of astronomy. These PhD candidates have been studying the impact of instructional innovations on student learning and systematically validating astronomy learning assessment instruments, both of which are important foundational work for the astronomy education research community. These efforts provide substantial weight to an argument that astronomy education research is maturing into a substantial disciplinary research field with many rich questions to pursue in the future.