...each class were allocated an equal amount of time during the school year?

Half days have their issues and we all understand that. Students are sometimes less likely to focus on instruction because they know they get to leave early. Teachers sometimes view them with dismay because periods are often shortened and very little effective instruction is possible (especially if students arrive 10-15 minutes late and stop working 5-10 minutes before the end of the period). It is for those reasons that we must balance the classes affected by a half day at school. While periods 1, 3, 4, and 5 are currently allocated 181 days of instructional time, periods 2, 6, and 7 are either shortened or cut during half-days, reducing class time by a full 7 days! How are teachers expected to keep up with the Planning and Scheduling Timeline for these classes if they are not provided with the same number of class days? A more balanced system would alternate half-days, alternating periods 1-3 (with a full period 2 block) and periods 4-7. This would at least guarantee that all classrooms were somewhat created equal.

Minimum number of hours of instruction per school year: http://www.pacode.com/secure/data/022/chapter11/s11.3.html

If you do the math on this one, 990 hours of instructional time divided by 180 days (including half-days) = 5.5 hours per day. So if a half-day provides roughly 2.66 hours of instructional time (they even get lunch time on half-days!), that means we are shortchanging our students by 2.833 * 7 = 19.833 hours over the course of the year. Nice job, school!