This is discussed in more detail below. This has considerable budgetary implications, as the increases in student numbers trigger additional state transfers to schools. For this reason it is being applied progressively over a five-year period with earlier implementation in deprived areas. In the first year the increase in compulsory education became operational in 30 municipalities, and countrywide implementation is scheduled for the 2012-13 school year. Full implementation is aimed for in the 2010-11 school year and will imply that at least for the first two grades the average class size will be at or below the norm in OECD countries. Since the 2007-08 school year a socio-economic index has been used to determine some of the budget allocation for primary schools.