I have found that constantly evaluating students during a practical exercise gets them ready for testing. As I go through the prelude to the exercise I ask questions as if I am a new student and unaware of what I should do next. If they are performing and get a result different than what is expected, it is a time for leading questions as to either why this result was achieved and what does it indicate. I have found that questions as an opportunity presents itself helps with the test scores by helping me evaluate my teaching skills and adjusting accordingly.