Enrolment rates are calculated by the UNESCO Institute for Statistics (UIS) from a combination of i) enrolment figures provided by Member States; and ii) population estimates from the UN Population Division. Using different population estimates in the calculation can result in varying enrolment rates and out-of-school rates. Moreover, the biennial revisions of UN population estimates have a direct effect on estimates of the rate and the number of out-of-school children, both past and present. If an accurate estimate of the population of a country is difficult to ascertain, determining the exact rate and number of out-of-school children within such country becomes a challenging task. Primary, lower secondary and upper secondary out-of-school rates are key thematic indicators of the UN Sustainable Development Goal 4 (SDG 4), which aims to “ensure inclusive and equitable quality education and promote lifelong learning opportunities for all.” Precise estimates for these indicators are essential so as to ensure that initiatives seeking to increase enrolment are directed at the correct target groups, and in order to guarantee that investments in the education sector are effective and efficient. The present work, therefore, entails an in-depth analysis and comparison of enrolment estimates, as well as of the rate and number of out-of-school children (OOSC) for primary and lower secondary school cohorts, followed by an explanation of observed differences and recommendations for improved assessment of school participation
