the main essential part of a curriculum or activity. It may often be mandatory with other elements then optional. Core + extension is a common if limited version of differentiation where only learners who have completed the core activity move on to other tasks. This approach needs to be planned and managed carefully to avoid problems. For example if extension tasks are serious learners may view it as punishment for success in the core whereas if they are more fun or involve pupil choice learners who struggle with the core may see themselves as being punished by missing out.  Similarly for workload reasons  extension activities are often unmarked leaving learners to question the value or point of what they have done.