A major reform of the education system took place in 1999, changing the overall organisational structure from 8 (primary school) + 4 (high school/liceum) years of education to 6 (primary) + 3 (junior high school, "gimnazjum") + 3 (senior high school, "liceum") years. The reform increased time spent on core subjects and delayed vocational study (lyceum) by one year. Poland's OECD educational rankings for reading and science shifted from being below average to being in the top 10, and to the top 15 for mathematics.