When first introducing the topic of waves to sixth-graders it is necessary to start with an explanation of what waves are and what travels with waves. Suggest that waves are vibrations that transfer energy without any matter, such as a solid or liquid, being transferred. A useful analogy is that of " the wave" in a football stadium, in which the wave goes around the stadium, but every spectator stays in place. Explain to them how light and sound travels in waves, and introduce the concept of wavelengths.
The next logical concepts to introduce are the parts of a wave. Start with explaining that the crest is the highest point in the wave and the trough is the lowest point. Then, define amplitude in terms they can understand, such as the height of which a crest reaches above the middle of the wave. It will be helpful to add visual adds. The notion of wavelength can also be addressed as the distance between two corresponding parts of a wave, such as from trough to trough or crest to crest.
A slightly more advanced topic is the result of adding waves together. Include the term "principle of superposition of waves" in the lesson, explaining that when waves overlap each other their amplitudes and crests add together, creating a different shape and properties to the waves. Waves can also cancel each other out if they are not in sync, called disturbance.
Introduce the concept of frequency to the students and explain how different waves differ in energy, frequency and wavelength. Then explain the electromagnetic spectrum, starting with the visible spectrum range. The idea that colors result from different wavelengths of light can be a hard notion for them to address. Find visual aids or computer simulations to help them visualize the idea. You may also introduce the Hertz unit, measured in wave cycles per second.