Q. Does Judaism still believe that “He who spares the rod hates his child” (Proverbs 13:24)?
A. In theory, Jewish law does believe in corporal punishment. The sentence you have quoted justifies parental discipline (cf. Prov. 19:18, “Chasten your child, for then there is hope”), though it is a rhetorical exaggeration to say that to avoid physical punishment is to hate the child. The second half of Prov. 13:24 says, “He who loves (his child) sometimes chastises him”.
However, it is better to try other methods, and to use corporal punishment only as a last resort. Otherwise a parent can end up being a hated bully. The same can be said about teachers – today, very rare – who use the strap or the cane on their pupils. The halachah allows a teacher to use a shoe latchet on a refractory child (BB 21a), but in modern education, corporal punishment is ill-advised and likely to invite pupil violence or at least court action.
The Torah refers to flogging with forty lashes (in practice, 39: Makk. 3:10) as a punishment for various offences (Deut. 25:2). This procedure remains on the statute book but its applicability has been legislated out of existence, especially since it could be imposed only if there were a Sanhedrin.
In certain cases of emergency, a Jewish court sometimes had the power to inflict corporal punishment as a deterrent, but this was hora’at sha’ah, a procedure required by the needs of the moment. A modern Beth Din does not flog anyone, and corporal punishment has been banned by Israeli law.