When using a repeated measures design, researchers must control the potential threat to internal validity referred to as?

When using a repeated measures design, researchers must control the potential threat to internal validity referred to as: practice effects

Practice effects refer to a method of data gathering where a subject is tested multiple times with similar method of testing.
By doing similar test over and over again, a researcher could guarantee the authenticity of the test result.

Basically create a schedule on what you need to study and stick with it