To sign test, form both hands into hooks or the ASL letter X sign (which is also the second half of the sign for ask or 'question'). Then bring down both 'X' hands as you spread them flat side by side, to signify paper. It is like saying a test or an exam is equivalent to questions on a paper.
Teach your toddler this sign when they are wondering why their older siblings are studying so hard. Depending on the type of test your kids are preparing for, whether it is a written or physical exam, remember that you can also teach and use the sign for drill.
This is a useful flash card taught best in conjunction with the other signs related to your child's test: whether this is academic, sports, or medical in nature.