One of the unique features of Alfred's Essentials of Music Theory is the Glossary of Terms and Symbols. A complete listing of all the terms and symbols in the lessons, it includes definitions of each term, plus spoken pronunciations, visual references and audio examples. Terms that are defined in the glossary are highlighted in blue text on the lesson screen. You can click on the term to get a pop-up definition of that term. The Educator version includes scored reviews that let you track student progress.
Teachers also have the ability to generate customized tests.