Student Resources
If you Google "online music resources", you can keep yourself busy for weeks checking out the hundreds of links you will discover. I just list a few websites here, but I periodically make updates.
classical.net: "The Internet's Premier Classical Music Source" - Comprehensive, with pages for basic repertoire, composers, books and scores, reviews and articles, and more.
musiclearningcommunity.com: Contains hundreds of learning games of varying levels that teach theory, ear training and rhythm.
funbrain.com: Offers games on composers, instruments, reading, and musical terms.
datadragon.com: Learning about and listening to different instruments; reading music; musical genres.
teoria.com: Great site containing exercises that develop musical knowledge and music theory skills, everything from note reading to ear training to chords to music theory reference knowledge.
quia.com/web: Students can test their music knowledge with quizzes, matches, concentration card games and other activities.
pbskids.org/chuck/index.html#/jazz: Elementary students can enjoy playing with an interactive Improvisation Station.
easymusictheory.com: Devoted to ear training and theory skills.
classicsforkids.com: Contains games, music lessons, and information on composers and classical music.
musick8kids.com: Fun music stuff just for kids.
iOS and Android Apps
Apps - they're everywhere. There's a ton of music apps, of widely-ranging quality, and there are more all the time. On an individual basis, I can help students find apps that work well for them in such categories as note reading, ear training, rhythm, improvisation, music theory, sightreading, etc.