If you are asked to explain what work-to-rule means, you can say the following:

“Until teachers and the District reach a settlement in our current negotiations, I will work during the hours required by our expired contract, but no more.  I have participated in programs and activities outside of these hours, as these provide enrichment for our children.  It needs to be understood, though, that this additional work occurs during my own personal time, and I don’t receive additional compensation for it.”