One of the main citation indexes is the Web of Science, accessible from the Columbia University Libraries Databases page. (Use the Cited Reference Search page to execute a citation search.) This is actually comprised of three sub-databases, the Social Sciences Citation Index (SSCI), the Arts and Humanities Citation Index (AHCI), and the Science Citation Index Expanded (SCI-EXPANDED), which can be searched separately or as a group, depending on how restricted or inclusive (by subject field) you want the search to be. The Cited Reference Search Help option provides basic guidance for constructing a search.
Another key citation index is Scopus, also accessible from the Columbia University Libraries Databases page. Neither the Web of Science nor Scopus is particularly strong in its coverage of the education literature, but as databases expressly designed to facilitate citation searching, they are definitely worth trying for this specialized type of research. The Scopus Help option provides basic guidance for the optimal use of the database.
A third very powerful resource for identifying works citing other works is Google Scholar (the Advanced Scholar Search mode provides the best means to customize your search). Google Scholar covers a huge number of publications across disciplines and in many cases provides direct links to the citing or cited documents.