There is growing concern about the mental wellbeing of young people, including how this is related to national tests. This is a particularly important policy issue in England, where it is claimed that the end of primary Key Stage 2 tests cause schools, pupils and teachers stress. I investigate this issue using data from the Millennium Cohort Study, comparing the wellbeing of pupils in England (measured around the point they are sitting their Key Stage 2 tests) to the rest of the UK (where Key Stage 2 tests are not taken). No evidence is found that the Key Stage 2 tests in England is associated with lower levels of happiness, enjoyment of school, self-esteem or children's mental wellbeing. Likewise, no evidence is found that children who are happier, more self-confident or with higher levels of wellbeing obtain higher Key Stage 2 test scores.