Diagnostic assessment supports student learning and achievement

Diagnostic assessment can be used to help teachers move beyond identifying what has not yet been learned by students towards planning instruction through which further progress can be supported.
Unesco's Addressing Learning Needs in the Asia-Pacific Region: Teachers’ Guide on Diagnostic Assessment was published in 2023. In the guide, diagnostic assessment is presented as a cyclical classroom process in which the need for assessment is identified, relevant evidence is collected through varied techniques, students’ learning needs are interpreted, findings are communicated constructively, and teaching is adapted accordingly.
In the educational literature, diagnostic assessment is regarded as a type of assessment for learning that is conducted at the beginning of a new teaching and learning sequence, such as at the start of an academic year, term, or lesson.
Through diagnostic assessment, students’ attainment in relation to curriculum learning expectations, their learning needs, and their readiness to develop further competencies are identified.
The assessment results are then used to tailor instruction to students’ learning needs. Diagnostic assessment is particularly important in contexts characterised by substantial learning gaps in relation to curriculum expectations, high levels of learning heterogeneity among students, and/or learning losses. Through this process, students’ current stages of learning can be identified, and appropriate support can be provided to facilitate their improvement and progress.
A connected cycle of setting learning goals, diagnosing learning, providing feedback, and adapting teaching is also described by the OECD (2025).
Therefore, the collection of assessment results alone should not be treated as sufficient for formative assessment; the evidence must be used to inform teaching and learning decisions.
According to Unesco's framework, the diagnostic-assessment cycle consists of five stages. First, during the planning stage, the learning goal and the prior knowledge or skills required by students are identified.
Second, evidence of learning is collected through appropriate tasks, questions, quizzes, student explanations, or samples of students’ work.
Third, the collected evidence is interpreted to identify patterns, misconceptions, and differences in students’ understanding. Fourth, clear and constructive feedback linked to the learning goal is provided to students.
Finally, teaching is adapted through reteaching, targeted practice, or learning-extension activities, as appropriate. However, the implementation of diagnostic assessment may be constrained by several challenges. These include limited planning time, large or diverse classes, assessment tasks that fail to reveal students’ reasoning, and insufficient opportunities for students to act on feedback.
The OECD recommends that evidence be interpreted accurately, individual learning needs be addressed, and sufficient opportunities be provided for students to use feedback to improve their learning.
Furthermore, successful implementation may be supported by the availability of appropriate school-level resources and institutional support.
In conclusion, diagnostic assessment is an important component of effective teaching, as it enables students’ readiness for new learning and specific learning gaps to be identified before instruction is planned and delivered.
By using assessment evidence to inform differentiated instruction, provide actionable feedback, and monitor progress, teachers can respond more effectively to individual differences and promote learner-centred teaching.
Nevertheless, the identification of learning gaps alone does not guarantee improved student achievement; meaningful progress depends on the extent to which assessment evidence is translated into appropriate instructional responses and targeted support.
Therefore, diagnostic assessment should be systematically integrated into regular teaching practices and supported through professional development, adequate planning time, and appropriate school-level resources.