Declining birth rates, for example, may drive down the demand for new teachers, and longer tertiary education can delay the entrance of teachers to the labour market. The ageing of teachers increases school costs, which limits the resources available to implement other initiatives at the school level (OECD, 2016: Education at a Glance 2016, indicator D5). The proportion is equal or more than 35% in the Czech Republic, Estonia, Hungary, the Netherlands, Portugal and the Slovak Republic. At the other end of the spectrum, in most countries with available data, 20% of pre-primary teachers are under the age of 30. Only in Australia, Korea, Japan, New' Zealand, Turkey and the United Kingdom does the proportion of pre-primary teachers under the age of 30 equal or exceed 25% (Figure 3.6).