Year round school would require raising teacher salaries by (25%?). Can school districts afford this particularly in the current downturn? Teachers tend to be paid less than other professionals. This is compensated for in some teachers' minds by the time off. Would year round teacher employment change the number and kind of person deciding to become a teacher?
In some school districts around here, YRS doesn't really mean YRS. What it means is that summer vacation is distributed throughout a full year. Teachers and students still spend the same amount of time in school.
UK does not use this system as far as I know. My cousin's been an elementary school teacher for 30 yrs and he's always had summer vacations.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13