Online Theory Practice

Here are a couple of websites that can be used to reinforce music theory principles:

http://musicteachersgames.com/

http://www.knowledgeadventure.com/games/musical-notes/

I'd recommend singing the notes/intervals as you go; it helps in ear training.

Learning Intervals--Song Association

Being able to identify intervals by both sight and by sound is very helpful. A good way to train your ear to identify intervals is by associating it with a song that begins with that interval. Here are some ideas:

Major 2nd:
Ascending--Happy Birthday
Descending--Mary Had a Little Lamb

Major 3rd:
Ascending--O When the Saints Come Marching In
Descending--Beethoven's 5th

Major 4th:
Ascending--Harry Potter
Descending--I've Been Working on the Railroad

Major 5th:
Ascending--Twinkle Twinkle Little Star
Descending--Feelings/Bring a Torch Jeanette Isabella

Major 6th:
Ascending--My Bonnie Lies Over the Ocean
Descending--Nobody Knows the Trouble I've Seen

Major 7th:
Ascending--Bali Hai
Descending--??? Any ideas???

Major 8th:
Ascending--Somewhere Over the Rainbow
Descending--There's No Business Like Show Business