Great article from

*Teaching Children Mathematics*,Volume 21, Issue 1, Page 18:**13 Rules that Expire**…avoid using these…

Overgeneralizing commonly accepted strategies, using imprecise vocabulary, and relying on tips and tricks that do not promote conceptual mathematical understanding can lead to misunderstanding later in students’ math careers.

These are good guidelines for teachers (and students of Math 260).

For example…

- You cannot take a bigger number from a smaller number.
- Addition and multiplication make numbers bigger.