My last school used to insist that staff were 'professionally dressed' on INSET days which I always thought was over the top. I have always thought that teaching staff should look professional when teaching though although women tended to get away with different styles of dress more than the men. I always wore a shirt and tie but never a jacket.......however rather amusingly my lanyard photo had a picture of me in a jacket! The jacket had been photoshopped on!!!