MusicTheory.net - theory tutorials, exercises
Music Tech Teacher - theory tutorials, worksheets, games
Teoria - theory tutorials, exercises
Diktus - free sight-reading and rhythmic dictation program
World of Music - listen to the sounds of 100 musical instruments
Classics for Kids: Composers - search for composers by name, country, and musical period
Music Academy Online: Composers - browse composers by musical period
The resources listed here allow students to explore the world of music including musical instruments, composers, repertoire, history, and theory.