Teachers are increasingly expected to adapt their teaching to students’ needs. This can be done by implementing differentiated instruction (DI) or assessment for learning (AfL). These concepts are regarded as two distinct approaches to identifying students’ needs and adapting instruction accordingly. In the current study, we aim to identify empirical similarities and differences in teacher knowledge and skills required for differentiated instruction and assessment for learning respectively. Based on combined insights from two cognitive task analyses (CTA’s), it appears that – in line with many other aspects of effective teaching – four phases are closely related for the task (either DI or AfL) as a whole: preparing a lesson series, preparing a lesson, enacting a lesson and, after this enactment, evaluating a lesson. The teacher skills required for DI and/or AfL in each of these phases are similar, however, the emphasis given to each skill differs in practice and this can be noted throughout all four interrelated phases. For AfL, the emphasis is on eliciting evidence during the lesson, for DI, the emphasis is on pro-active alignment of instruction and activities, based on students’ needs. Since teachers need the same underlying skills to be able to perform either DI or AfL, we can hypothesize that teachers who are proficient at either DI or AfL, will also be able to develop and implement AfL or DI in practice.