My high school has been on block scheduling for three years. We have four periods a day and teach three on one day and two the next. Two of the eight periods are for planning and one of the eight periods is a school wide study hall. There are a lot of things I like about this. Teachers have a little more planning time and you only have to plan for, at most, three classes at a time. The longer periods are less stressful and we don't have to switch gears so often. Students like it a lot because they don't have to prepare for as many classes as once. It is definitely easier!
Here are the things I don't like about it. There is a definite lack of continuity and children - Yes, 14 through 18 year olds are still children in many ways. - generally are not good a self discipline and time scheduling. The students want no more than the "standard" amount of homework even though they are supposedly preparing twice as much content. They think the homework requirements and the speed at which material is covered should not have changed from the every-class, every-day schedule. We lost a significant amount of class time with this change. It actually worked out to fifteen class periods per course! Frankly, I don't think it has helped a single child to perform at a higher level. The honors students are unaffected by it and the slow students are difinitely hurt by it.
I understand that the longer periods are truly wonderful for lab classes. When I went to high school - back in the dark ages - our science classes met seven periods a week. Three days were single periods and lab days were double periods. I attended a large - 1500 students - school so the scheduling must have been complicated, but it was done.
I should mention one truly wonderful thing about our block system. The school wide study hall permits time for individual help and making up work. Of course, this means that you must run your study hall with an iron hand so that work can take place, but the benefits are worth it.
Our school system is seriously considering the four by four approach. (An entire course in "one" semester.) I am very hesitant about this. I would love to hear some concrete experiences.