At the end of the last academic year I was asked if I could work 2 afternoons a week on top of my 5 mornings. I said I could easily do Thursdays but Wednesdays would be difficult because of childcare issues and that I could only do so on the proviso that I was able to leave no later than 3:30pm. This was agreed, but unfortunately not put in writing. My new head (who the agreement was made with) has now said that I have to attend staff meetings on a Wednesday after school. I have asked if we can have them at lunch (like we used to) or on another day, but all she keeps saying is that I have an obligation to come to 0.7 of them, on a Wednesday. What can I do?