In version 1.9.x of Moodle it is possible to hide activities for certain groups of students in a course. This is especially handy for a "team taught" (multiple teachers in one course who have self-contained classrooms with their own students on a daily basis). This can allow activites to be graded but only for a single teachers students as well as provide other differentiated instruction (audio files for those students with auditory intelligence, as an example).
Here's how:
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