Some concepts are too abstract to be reliably learned from representational sources. For example, if students are instructed to read a manual on the correct way to use litmus paper in order to determine whether a liquid is a base, neutral or an acid, it is probable that several of the students may not understand the written directions. What would be a more effective instructional strategy that would teach the students how to correctly use litmus paper to determine the acidity (pH) of a given liquid?