If you are purely into research about educational theory and curriculum development, then a PhD. in educational psychology is the way to go, but you will not be able to get any sort of licensure to practice. If you are interested in being able to do practice and research about interventions, then a PhD. in School Psychology from an APA/NASP-accredited program is a good way to go if you want the flexibility. If you are interested interested in purely practicing in a school setting, then getting a EdS. or a master's level equivalent from a NASP-accredited program will give you that; however, you can't do private practice at that level, only at the PhD. level with licensure as a psychologist can you do that. I don't know how much redeeming value a master's in educational psych would have unless you plan on applying to doc programs in the future.