It is known that the reading performance of disadvantaged students is lower when compared to non-disadvantaged students. It has always been discussed that being disadvantaged affects teachers' bias in scoring students' reading performance. Therefore, the existence and effect of the teacher factor in the low level of reading performance of students in disadvantaged groups is worth investigating. The reading comprehension skills of disadvantaged and non-disadvantaged fourth grade primary school students were assessed in this study. Moreover, whether the classroom teachers were biased in scoring the reading comprehension skills of the disadvantaged students were also investigated. The reading comprehension skills of 48 students, 13 of whom were disadvantaged and 35 were non-disadvantaged, were assessed by three classroom teachers (raters) using an analytical rubric. The data were analyzed using the Many-facet Rasch measurement model. It was found that the classroom teachers were biased in evaluating the reading comprehension skills of disadvantaged students. Likewise, the reading comprehension levels of the non-disadvantaged students were higher than the disadvantaged students.