What is the test for using corporal punishment in school?

In Cooper v. McJunkin, 4 Ind., 240, it was said: A teacher, in the exercise of the power of corporal punishment, must not make such power a pretext for cruelty and oppression; but the cause must be sufficient, the instrument suitable, and the manner and extent of the correction, the part of the person to which it is applied, and the temper in which it is inflicted, should be distinguished with the kindness, prudence, and propriety which becomes the station.

In Gardner v. Bygrave (1889) 53 J.P. 743, 6 T.L.R. 23 : The master of a board school was charged with assaulting a pupil by caning him on the hand, and the magistrate being of the opinion that the caning on the hand was attended by the risk of serious injury to the hand, convicted the defendant, although the punishment was not excessive and there was no evidence of any serious injury having resulted in the particular case. On appeal it was held that the reason given by the magistrate for convicting was insufficient, and the conviction was quashed.