This brings down the average performance of the country (see Figure 3.3). Moreover, the very small proportion of students (0.9%) who achieve the highest levels in science, mathematics, or reading (levels 5 or 6), which is far below the average across OECD countries (15%), means that there is a very small pool of young school-leavers who are well prepared to pursue higher level technical and scientific education, a major challenge for a country seeking to develop its knowledge-based industries. Nearly one third (31%) of 15-year-olds have repeated a year in Costa Rica, above all OECD countries except Mexico (see Figure 3.4). However, grade repetition rates in primary school almost halved between 2005 and 2014, from 7.5% to 4.3%, as a result of new rules restricting its usage (see Chapter 4).