SchoolCal offers an incredibly simple interface with which to enter any and ALL dates associated with a typical school year into an iCal calendar.
You can use either an existing calendar, or SchoolCal will create a new one for you!
In either a single session, or multiple sessions, you can create iCal Events for all the major vacation periods (Thanksgiving, Christmas, Midwinter, Spring), as well as schedule Snow Days, Late Arrival Days, No School Days, Conference Days, or whatever other type of school-associated event you wish. No data is lost in between launches; you can take as long as you need to build the calendar data before committing it to iCal.
SchoolCal is just what you need to keep yourself, your family, and any student in your life on track, and on time!