I get this question a lot, and it really takes a keen eye to figure out if the student is bluffing or is genuinely comprehending a teacher's verbal class directions/information. Here is one example.
Say there is a student with HL sitting in the 3rd row to the far left, right near where the teacher does the teaching from, and the teacher tells everyone to get their science books out and turn to page 24. You'll see one of two actions that lets the teacher know whether the student is bluffing or not:
1) The student automatically gets his/her book out and turns to page 24
2) The student looks around to the classmates before he/she begins to get science book opened.
Now, teachers, you'll be able to tell whether or not your student is bluffing.
