The Waterline Principle, and What it Means for Children's Interactive Design

Designed for early childhood classroom room arrangement, the "waterline principle" means that you set up an environment for children where everything they can reach is "on limits" (rather than off limits). You create an imaginary line that represents the tallest child's reach. All toys and materials that are above that line should be out of site, and out of mind, as to not tease a child with choices they can't have. Everything below the line should be fair game for use.

What does this mean for children's interactive designers?

First, designers need to take a global look at their experience, starting with the packaging and installation and ending with the exit routines. Most trouble happens when starting or ending an interactive experience.

Typing in a registration code or reading an acceptable use policy is above the complexity waterline. Preferences such as network settings or your computer's clock are the equivalent of your classroom's supply closet. You don't want children to be playing in there. So they need to be out of site, and beyond a child's line of site. If you have preferences, say for changing players or for adjusting the sound, you need to make sure they are usable by the intended audience. Otherwise, you open the possibility for frustration.

Instead of the tallest child, think about the most bored and curious child. They're the ones that are likely to test the limits of your interface.