Handbooks contain short entries that summarize and define complex research and also highlights important scholars. Use handbooks to get background information, define theories, and find foundational scholars. Scholarly articles published in academic journals present a very small sliver of a large and often complex research topic, so handbooks can be an excellent way to get the bigger picture.
Think of handbooks as a credible Wikipedia article - it's written by an expert and included in an edited book, and it's a helpful summary of dense foundational knowledge that will help you build your understanding.
Use the below databases to search through thousands of encyclopedias and handbooks at once.
The Oxford Encyclopedia of Qualitative Research Methods in Education by 
The Sage Handbook of Inclusion and Diversity in Education by 
The Wiley Handbook of Learning Technology by 
The Handbook of Educational Theories by 
The Oxford Handbook of Qualitative Research by