The summer-off argument has been used in many countries and since I know some teachers now it is a pretty shitty argument as most of the 'summer vacation' is filled with learning (required), creating next years curriculum due to changes in the requirements and helping the less-well-off children get through. On average they do get a bit more off-time in the summer, but also work considerable longer hours per day and nights (speaking to parents, yay!) than most office workers.