There are well-documented concerns in international research about the reliability of school-based assessment related to the consistency and quality of marking and judgement at the school level, and alignment with agreed national standards or curricular outcomes (OECD, 2026[36]). Evidence from different education systems demonstrates how far teacher grades may diverge from expected national learning standards. For example, a national investigation in Sweden has recently concluded that, despite multiple national initiatives to promote greater comparability in teachers’ grades, grades from teacher-based assessment do not represent the same level of knowledge and skills across schools (Skolverket, 2020[38]). While some differences between external examinations and teacher-based assessment are natural, as they assess different competencies, consistent divergences across systems underscore the inherent challenges of teacher-based assessment for ensuring that all learners are progressing in line with national expectations.
To promote the quality of SBA tasks and the reliability of assessment judgements, South Africa has a developed system of quality control and social moderation at school, district and province level. For all class tests, teachers engage in collective, social moderation by sampling several scripts to discuss the marking to promote standardised marking. A sample of marked scripts are then moderated by the school’s moderator. Schools keep a record of their assessment tasks and internal moderation reports which may be checked at the district and province level (DBE, 2023[34]).
Despite the significant investment in social moderation in South Africa, evidence suggests that there are wide variations between SBA marking and national standards. Since 2015, the Western Cape has been the only province to use full cohort, annual learner assessments. The data from the standardised learner assessments in the Western Cape suggests that there are significant variations between SBA and standardised assessment results. For example, in 2022 in Grade 3 in mathematics, the SBA score distribution was concentrated around 60‑70% with a peak near 65%. In contrast, systemic test scores based on the same learning standards (i.e. the Western Cape’s standardised assessment) were concentrated at lower levels, with most scores between about 35% and 50% and a peak around 40%. The contrast between results suggests that while most learners were not reaching the required standard, their teachers believed that they were. (World Bank, 2024[39]). The findings from Grade 3 in the Western Cape are mirrored by similar research based on SBA in Grades 11-12 and examination results from the NSC in Grade 12. This research has found significant differences between SBA and the external NSC marks, with school-based marks often being consistently higher than NSC marks (van der Berg and Shepherd, 2009[40]). Research also suggests that disparities between SBAs and external exams do not occur evenly across schools, with more socially disadvantaged schools demonstrating greater disparities (where school-based marks exceed external exam results by greater amounts) on average (van de Berg et al., 2023[41]; Euston-Brown, 2025[42]).
Given the complexities associated with school-based assessment, most OECD countries implement national assessments (28 out of 32 countries, for lower secondary education) to provide teachers – and the system as a whole – with reliable assessment data (see Figure A B.1). Among the countries with national assessment, the majority (18 out of 28) organise them annually across the full cohort. In cases where national assessments are only sat by a sample of learners, these national assessments are frequently organised annually (5 out of 10). By sampling the full cohort and/or implementing national assessments annually, these countries have accurate, representative data that they can use to closely monitor trends and understand the strengths and challenges of teaching and learning in their system.