1) According to INEE, the recommended maximum class size for primary grades is 40 children per teacher.
2) If there are big differences between student populations in different grade levels, you might need to calculate it separately for different grades (e.g. average class size for first cycle: grade 1-5 and for second cycle: grade 6-9) to get a more accurate picture.
3) If a school suffers from low attendance rates, then the indicator should be calculated based on the number of attending students (instead of enrolled ones).
4) Teacher to pupil ratio (TPR) is frequently used to serve the same purpose as average class size. Using an average class size instead of TPR makes for a more straightforward calculation and avoids having to deal with issues of part-time teaching, school-shifts, multi-grade classes and other practices. (As the number of part-time teachers should be converted to ‘full-time equivalent’ teachers; a double-shift teacher is to be counted twice, etc.).