Present the abstract idea to the class. Write it on the board, and discuss its definition or definitions. For example, if you are teaching students about allusion in literature, provide a definition, write it on the board and make sure everyone understands it.
Pass out a hard copy of a text or situation that exemplifies the concept you are teaching. For example, if you are discussing allusion, distribute a piece of literature that is allusive, such as a poem that references Greek mythology or a biblical story.
Have the students read the example. Then break the class into small groups. Have students find the allusions in the piece of writing together and then present them to the class. Ask them to discuss why and how their example functions as allusion.
Have the students come up with their own examples of allusions in contemporary music, film or other media. Ask them to present these examples, then explain why they are allusive and what other work they refer to.
Assign the class a related homework task. Have them choose an abstract concept that relates to the course's field of study. For example, if it is a literature class, ask them to choose a literary theory or concept from their textbook. Ask them to prepare a mini lesson that teaches their classmates this concept using a concrete example. Have them record in their notebooks how this process affected their understanding of this concept.