Addison Central School District, Addison Central School District Calendar, academic calendar, school year dates, first day of school, last day of school, holidays, winter break, spring break, summer break, non-instructional days, teacher workdays, professional development days, school closures, term dates, important dates, district schedule, students, staff, events, academic schedule https://nycschoolcalendars.com/addison-central-school-district/2025-2026