While I was being observed by my principal only one child raised her hand to answer a question.  When I called on her she said that she had to go to the lavatory.  I then established the time-out (T) hand signal that students used when they had to go to the restroom.

Ten Top Tips: Lesson Observations | The Creative Education Blog

Observation Tip
from Professor Tom Whitby

Tell your students to raise hands at every question.
Right hand if they know the answer. Left hand if they do not know the answer.