Final answer:
The nurse is using the education principle of 'stimulating recall of prior learning' by reviewing previously taught information about diabetes physiology before introducing new content.
Step-by-step explanation:
The nurse teaching a class to clients with diabetes is using the principle of effective education known as stimulating recall of prior learning. By reviewing the basic physiology of diabetes that was taught in a previous class, the nurse is activating the students' prior knowledge, which can make new information more meaningful and easier to understand. This approach helps in forming connections between what they have already learned and the new content being introduced, such as the management of diabetes through lifestyle changes, blood-sugar monitoring, and medication adherence.