Camilla Rjosk, Nele McElvany, Yvonne Anders, Michael Becker

• The present study investigates diagnostic skills of German teachers in estimating basic reading capacities of sixth graders and the way they relate to achievement heterogeneity of the judged student group and to students' language background. The data were obtained from a sample of 39 German teachers and their classes in the context of the Berlin Longitudinal Reading Study. Judgements on different levels were analysed (achievement of sixth graders in general and of individual students). Diagnostic skills were investigated using different indicators: the personal judgement error and tendency and the accuracy in identifying achievement differences between individual students (rank component). The accuracy in estimating reading capacities of students with and without a different language background was investigated by means of achievement level matched pairs. The outcomes indicated, among others, an overestimation of students' general achievement level and on average an acceptable accuracy in identifying achievement differences betweenThe present study investigates diagnostic skills of German teachers in estimating basic reading capacities of sixth graders and the way they relate to achievement heterogeneity of the judged student group and to students' language background. The data were obtained from a sample of 39 German teachers and their classes in the context of the Berlin Longitudinal Reading Study. Judgements on different levels were analysed (achievement of sixth graders in general and of individual students). Diagnostic skills were investigated using different indicators: the personal judgement error and tendency and the accuracy in identifying achievement differences between individual students (rank component). The accuracy in estimating reading capacities of students with and without a different language background was investigated by means of achievement level matched pairs. The outcomes indicated, among others, an overestimation of students' general achievement level and on average an acceptable accuracy in identifying achievement differences between individual students. They showed equal difficulties in judging performances of students with and without a different language background.…