In Brief: 
Students say thirds with tossing cards and the suspenseful "pea under the walnut shell" game
To begin to memorize thirds
Prerequisite Concepts: 
The musical alphabet
Teacher's Role: 
Toss alphabet cards (or do re mi cards) in thirds order in front of your students. This game gently reminds your students to pay attention to you without your having to ask for it. (The pink do re mi cards in the video are only available in Spain)
Usually once is enough, but may be repeated before playing other games