According to the Ministry of Education a student has not arrived at school until they attend at least one day in that school in the new school year.
But it is very important to keep track of No-Show students
To do so you can use the Consecutive Absent Report to find these No-Show students, but to force them to show up on this report you MUST click the Include absences prior to student start date, this button is needed because they have not as yet shown up at your school for this school year.