Age Range: 7 and up (approximately, non-readers will need assistance)
ClickScholar MaryAnna Cashmore suggested this commercial website where you can access the basic facts of music theory for FREE. Learn or brush up on the names of music staffs, lines and spaces, notes, key signatures, major and minor scales, time signatures and more. The site is divided into two helpful sections that include Music Theory I and Music Theory II.
When you get to the site, you will land on the first page of "Music Theory I." You'll see a brief description of one topic on music theory. Look at the menu on the left side of the screen to access all of the material in this category from learning the music alphabet to identifying keyboard keys, to learning about the "Circle of Fifths."
When you are through exploring that section click on "Music Theory II" on the menu to access the free information on Thirds, Root Positions, Arpeggio, Triads, and more.
This site is really a glossary of music terminology - and the simple definitions and explanations make it easy to understand. There are no bells and whistles and no drills - just bare bones basic music facts.