This paper explores the effects of in-class level differentiation by making innovative use of an interactive whiteboard (SMARTboard) on math proficiency. Therefore, we evaluate the use of SMARTboard in class, in combination with teacher training, using a randomized field experiment among 199 pre-vocational students in 7th-grade in the Netherlands. During six weeks, students in the intervention group participated in math classes in which the SMARTboard was used to apply level differentiation. The teachers of these classes received a specific training (Technological Pedagogical and Content Knowledge” (TPACK)) in using the SMARTboard in class. Control classes were taught by teachers without the training, who did not use the SMARTboard in class. The results show that level differentiation in class, which was possible because of the efficient use of the SMARTboard, significantly increases math proficiency with 0.25 points.