When I went to school many years ago (98-03 - i'll leave you to decide which century) we went Monday to Friday. Registration was 8.55-9.10. First lesson was 9.10-10.10, first break was 10.10-10.30, second and third lessons were 10.30-12.30, lunch was 50 minutes, afternoon registration was 1.20-1.30, then two lessons from 1.30-3.30. Then we went home. Now I think with the way the working world is they should have to go five days, but I'd change it to 9-4, some schools do operate that way anyway so it wouldn't be a major upheavel. I, like Zorak would cut down on the holidays. I'd start school on the first Monday of September until the nearest normal weekday to Christmas eve, then let them have until like the 4th january off, something around that date. Then off till easter Maundy Thursday till the Tuesday after Easter Monday. Then off until the last Friday in July until the aforementioned September date.
On the idea of a four day week, i don't agree with it because I don't think it'd be of any use, plus they have 'teacher training days' anyway.
One thing I would do is have schoolkids do a trade at school, or at least start one in year 11 so they have something to go into.