Encyclopedias, guides and handbooks (also called "reference sources") are excellent sources to consult when you are starting your research.
They can clarify concepts and/or theories and provide important terminology and the names of related, theories, relevant theorists or seminal works related to that particular topic.
Encyclopedia of Educational Philosophy and Theory [ONLINE] by 
Encyclopedia of Education and Human Development [ONLINE] by 
Sociology of Education: an A-Z Guide [ONLINE] by 
Rethinking Education: Whose knowledge is it anyway? [ONLINE] by 
An Introduction to the History of Educational Theories [ONLINE] by 
Philosophical Perspectives on Compulsory Education [ONLINE] by 
Pedagogy, Praxis and Purpose in Education [ONLINE] by 
Encyclopedia of the Social and Cultural Foundations of Education [ONLINE] by 
The Handbook of Dewey's Educational Theory and Practice [ONLINE] by 
Encyclopedia of Terminology for Educational Communications and Technology [ONLINE] by 
Evidence-Based Approaches to Becoming a Culturally Responsive Educator {ONLINE] by 
Igniting Wonder, Reflection, and Change in Our Schools: an educator's guide to using authentic stories [ONLINE] by 
Culturally Responsive Teaching: theory, research, and practice [ONLINE] by 
Forms of Practitioner Reflexivity: critical, conversational, and arts-based approaches [ONLINE] by 
The Courage to Teach Guide for Reflection and Renewal [ONLINE] by 
