Data generally refer to the school year 2020/21. Statistics that relate participation data to population data are published for the reference date that was used by national authorities for these statistics. It is assumed that age references in the enrolment data refer to 1 January of the reference year. For Australia, 30 June is used as the reference date for ages in both enrolments and population data for all education levels except pre-primary, which has the reference date 1 July for enrolments. For Japan, 1 April is used as the reference date for ages in population data and 1 May is used as the reference date for enrolments. For the United States, 1 October is used as the reference date for ages in enrolments data, but the reference date for ages in population data is 31 October.