Use spreadsheets to draw lots for two groups of invigilators in the examination room.

Find an empty cell (such as K 1) outside the invigilation schedule and fill in the name of the teacher to be inquired.

Suppose the teacher's name area in your invigilation arrangement is A2:H40.

Starting with A2, select A2:H40.

Conditional Formatting

Use the formula to determine the cell to set.

Conditional formula

=a2=$K$ 1

Also set the cell fill shading.

Do it.