I have, we were running late, I had an important appointment and just let them know. Easy as. DS1 has had issues with not wanting to go to schooland so will refuse to get into his school clothes (he had actually refused to wear his pjs and get out of his after school clothes as well) so he went in his dirty clothes. The school obviously wasn't impressed until I explained the situation to them and they told me next time to send him as is with a spare set of clothes, same as when he purposely dirties his clothes so he doesn't have to go (3 shirts in one hour. I was not impressed).