The total number of days of student attendance divided by the total number of days in the regular school year. A student attending every day would equal one ADA. ADA is not the same as enrollment, which is the number of students enrolled in each school and district. (Enrollment is determined by counting students on a given day in October.) ADA usually is lower than enrollment due to factors such as students moving, dropping out, or staying home due to illness. The state uses a school district’s ADA to determine its funding.