Simplicity takes intentionality. The natural bent is to try to cram as much information into a lesson as possible. Rabbit trails beckon.
Resist the urge. Great communicators with kids (and adults) know how to drive one key truth home. This is not "shallow" teaching, this is "focused" teaching.
Instead of sharing several truths in one way, share one truth on several ways.
This one step will move what you teach from kids' short term memory to their long term memory.
