* School attendance records: This is the primary source. These records are usually kept electronically or in a physical register, and will show the dates the student was present and absent. These records might be maintained by the school's administrative office, the student's teacher, or a designated attendance clerk.
* Absence notes/excuses: Parents or guardians often provide notes or documentation explaining absences (doctor's notes, etc.). These would be filed alongside the attendance records, either physically or digitally.
* School calendar: To accurately calculate the total number of absences, you need to know the total number of school days within the relevant period (e.g., semester, school year). The school calendar will specify scheduled school days, excluding weekends and holidays.
The exact location of these records will vary depending on the school and its record-keeping system. You would likely need permission to access this information due to student privacy concerns (FERPA in the US).