Something used by students to study in bed (4)

I believe the answer is:

crib

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'bed' is the definition.
(bed for a child)

I can't explain the rest of the clue.

(Other definitions for crib that I've seen before include "Translation cheat; fodder rack" , "Nativity model" , "A baby's cot in America" , "Manger; cheat by copying" , "cheat in school" .)

I've seen this clue in The Guardian.

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