A teacher wants students to learn the concept "red." She puts three red triangles on the felt board. Here are the possible interpretations: red is red; red is triangles; red is only red triangles (not squares); red is triangles on the feltboard; red is anything on the felt board. Without further examples of what red is and is not, many students would—quite reasonably—pick up a wrong interpretation.
What they learn is entirely consistent with what you teach. It's not that they have funny heads. It's that you're a funny teacher.
January 9, 2007
On teaching misrules
Here's a good example of how teachers sometimes inintentionally teach misrules: