This study focused on the differentiation practices of second- and third-grade teachers in mathematics and reading comprehension lessons. Preconditions for differentiation, classroom organization, and how teachers dealt with students of different ability levels were investigated through observations, using a time-sampling instrument. Data of 43 teachers, from 18 schools, show the importance of taking context factors into account. The study also focused on how students of four different performance levels were addressed by their teachers. It was found that teachers mostly adapted teaching to the relatively weak performing students in their class by addressing them more often, in a content-related way. Relatively advanced students received additional attention less often.