On average, 13 % of 15-year-olds in the OECD have repeated at least one grade in primary or secondary school …

„On average, 13 % of 15-year-olds in the OECD have repeated at least one grade in primary or secondary school. […] In France, Luxembourg, Portugal or Spain, the rate of grade repetition is as high as 35 %.“

OECD (Hrsg.), „Trends Shaping Education 2017“ (2017), Spotlight 8, S. 5