Before using an X-Acto Knife with students you need to make sure that they are prepared to use the tool in a safe way to protect themselves and their peers. This Xacto Knife PDF document includes a definition, 16 rules for use, and procedures for clean up.
Ideas for use:
Have students take notes on the 16 rules and show them to you before they are allowed to use the Xacto Knives.
Give a demonstration after going over the notes as an extra safety precaution.