The claim that teachers' assessments cannot be trusted ("Teacher assessment too prone to bias", November 5), so that we have to rely solely on the results of external tests, contradicts the evidence of several systematic studies, in England and elsewhere. These have shown that high levels of reliability can be attained, matching that of external tests.
However, there is also evidence that professional development in assessment skills is essential. This has to include development of procedures within and between schools so that teachers can justify their judgments with evidence that is shared, and audited.
The issue is an important one. In the school years when there are no mandatory external tests, teachers' assessments are the main source of guidance for decisions about the subject each pupil should study in subsequent school years. In our work with teachers in a few schools, a group of us at King's found they welcomed collaboration to enhance the quality of their summative assessments.
Paul Black, Emeritus professor of education, King's College London.