Two essential targets a fully-realised idea of a wave are superposition and the transmission of information. What might serve as experiential resources with affordances that provide credible and fruitful learning pathways to these two ideas?
Steps might be a useful prototype for the superposition facet of waves as they necessarily entangle time and space with the idea of the speed of progression. And one can be more-or-less in-or-out of step, which serves as a fruitful precursor to the idea of phase. Add the idea of varying amplitude, and so of varying contribution from a path or source and a learning pathway to superposition becomes conceivable.
A second building block is the idea of a mimic, or more demotically, a
copy-cat. Just as I can mimic the action of another, so I can imagine a detector mimicking the action of a source after a delay, providing the resources to build the idea of a wave on top of well-established source-medium-detector model used in introducing seeing and hearing.
Beside this pair the traditional distinction between longitudinal and transverse remains much less important: only distinguishing two sub-genre, and not serving to distinguish the genre from others.