Popsicle stick harmonica

Materials

• 2 Popsicle or craft sticks
• 1 large rubber band
• 2 small rubber bands (or loom elastic bands)
• 2 small straw pieces (about the width of the craft sticks)

Take your larger, thicker rubber band and wrap it lengthwise around 1 craft stick.
Place one of the straw pieces under the thicker rubber band at one end of and then place one on top at the opposite end.
Place your second craft stick on top of the first craft stick. This will cover the thicker rubber band and the straw pieces.
Rubber band one end together, then rubber band the second end with the smaller rubber bands.

We found a Sophie's World craft video on YouTube that walked us through the steps we just described that can help. 

Sophie's World Kazoo Craft

Vibrations need a medium like air to travel and produce sound that finally reaches our ears. Higher pitched sounds are created by waves with a higher frequency. The pitch, or frequency, produced is equal to the number of times per second (hertz) that the rubber band vibrates. You can change the pitch of your harmonica by moving the lolly sticks or blowing air at different speeds. When the lolly sticks are closer together, the pitch will be higher.
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Airflow around the rubber band also affects the sound. The air flowing above and below causes the rubber band between the craft sticks to vibrate due to disturbance in the air. Like most objects, the rubber band has a natural frequency at which it vibrates most easily.

Carmelo the Science Fellow also has another style of harmonica made with rubber bands, card stock, and tongue depressors (or craft sticks).

Carmelo the Science Fellow Harmonica