I have this as part of my policies:

"I will make every effort to assist in potty training along with your efforts at home. I will begin when the child appears to be ready for this step. Usually between 2-3 years old, when they can verbally tell me that they have to go potty. I will ask that your child wear pull-ups during this period of potty training and I will only attempt to potty train if the child is being potty trained at home as well. Please do not bring your child in pull-ups unless they are starting to use the potty regularly."

Hope that helps.