In teacher research, causal attributions of low achievement have been proven to be predictive of teachers' efforts to provide optimal learning contexts for all students. In most studies, however, attributions have been studied as a between-teacher variable rather than a within-teacher variable assuming that teachers' responses to low achievement are stable for different students in one classroom. To understand teachers' variation of their behaviour towards different low achieving students it would seem worthwhile to identify within-teacher variation of causal attributions. In this study, we analysed the within-teacher variance of attributions of 64 secondary school teachers. Analyses of attribution ratings for three low performing students per teacher showed that, in general, the amount of within-teacher variance was very large, although the within-teacher variance differed among attributions. It can be concluded that teachers' causal attributions of low performance should be investigated as within-teacher variables because they vary between low achieving students.