Green’s Dictionary of Slang

one who uses some form of illicit aid when taking examinations or similar tests.

1899		Kipling ‘The Impressionists’ in Complete Stalky & Co. (1987) 102: ‘Serve you jolly well right,’ said Orrin, ‘you cribbers!’.
1900		E.H. Babbitt ‘College Words and Phrases’ in DN II:i 30: cribber, n. One who is always borrowing.
1914		‘Ian Hay’ Lighter Side of School Life 140: He is a rare bird, the confirmed cribber, with his algebraical formulae written on his finger-nails, and history notes attached to unreliable elastic arrangements which shoot up his sleeve out of reach at critical moments.
1931		P. Stevenson Gospel According to St Luke’s 154: The whole point is there won’t be any cribbers if we’re on our honor.
1959		I. & P. Opie Lore and Lang. of Schoolchildren (1977) 202: A copy-cat is not, however, one who copies off, or over-looks, another person’s work. Such a person is almost always a ‘cribber’.