Most learners in South African schools missed at least three-quarters of a school year over the course of 2020 and 2021, due to the Covid-19 pandemic, lockdowns, school closures and rotational timetables that were introduced to maintain social distancing in classrooms. These lost school days are known to have affected learning, but lack of data has thus far limited attempts at measuring learning losses. The only two studies measuring learning loss thus far were limited to fairly small samples of learners in relatively poor schools, to reading and only to the lower grades.This study considers a much larger sample, virtually all public schools in the Western Cape, across Grades 3, 6 and 9 in both Language and Mathematics, comparing 2021 performance with that in 2019. It thus offers a more comprehensive picture of learning losses that also has relevance in other parts of South Africa, particularly when also considering patterns across quintiles and schools with different language policies.The findings are indeed extremely concerning: Losses in Mathematics tend to be the largest (consistent with international experience), and even when using a relatively conservative measure (assuming that a year’s learning is as much as 40% of a standard deviation in primary and 30% in secondary schools), the losses indicate that learners in 2021 had fallen more than a year of learning behind learners in the same grade in 2019. In Language, losses are smaller, around three-quarters of a year equivalent in terms of learning.Most South African learners are taught in their home langue in the Foundation Phase (up to Grade 3), but then transition to being taught through the medium of English for all subjects (except their home language) in Grade 4 and beyond. The pandemic has made this difficult language transition even more difficult. In Grade 6 Language, learners are tested in the school’s LOLT (Language of Learning and Teaching), which could be either English or Afrikaans. Performance declines in Language in Grade 6 between 2019 and 2021 are much larger in schools that experience this language transition. These same schools also experienced the largest learning losses in Mathematics performance in Grade 6, perhaps because poor language skills also limit learning in Mathematics.Two policy areas require special attention: The first is to find more time for Mathematics, to overcome the deficit that has accumulated during the Covid years. For instance, Grade 9 learners in 2021 were performing more than a year behind Grade 9 learners two years earlier, so they must catch up a full year before they write matric. This requires that they progress more than four years in the three years before they write matric. In Language, the big challenge is to ensure that reading has been mastered in the Foundation Phase, while at the same time giving urgent attention to ease the language transition. Weak reading skills and English vocabulary can inhibit all further learning for the majority of learners who have to make this language transition