Using linked data from the Millennium Cohort Study and National Pupil Database (N = 8,139), this study examined how the timing of school absences (years 1 to 11 between 2006 and 2017) affects achievement at the end of compulsory schooling in England. Absences during any school year are harmful to student achievement. However, absences in years 6 (final primary school year) to 10 (penultimate year of compulsory schooling) are between 1.6 and 2.0 times more detrimental to academic performance than in other years. Every school year, authorized absences hurt academic performance as much as unauthorized absences. To test the robustness of our findings, we used comparable data and analytic methods for Wales and reached the same conclusions. Our study points to the importance of addressing absences at every stage of the school year to improve educational achievement for all students, particularly at the transitional stages of primary to secondary school.