see annex for notes wwwoecdorgedueaghtm education systems in oecd and most g countries now provide universal access to basic education such that both preprimary and upper secondary education are becoming universal in most countries see also indicator c the expansion of upper secondary education has been driven by both increasing demand and policy changes ranging from a more flexible curriculum and a reshaping of vocational studies to efforts to expand access to education to the entire population while the same changes have been made to tertiary education participation rates at this higher level of education are significantly lower