Final answer:
The experimental design principle exemplified by repeating the experiment multiple times is Replication, which confirms consistency and reliability of the experimental results.
Step-by-step explanation:
The principle of experimental design being described when repeating an experiment multiple times with different teachers or at different times of the year is Replication. Replication is a core component of a scientific experiment, alongside other principles such as randomization and control. By replicating the experiment, the researchers can confirm that the results are consistent and not due to chance, thus providing more reliable data. This consistency helps to ensure the effect observed (in this case, the time of day science class is taught on test scores) is likely due to the variable being studied rather than other extraneous factors.