Experts, counselors, and parents who are advocates of spanking as a form of behavioral correction, on the whole, agree that spanking is most effective at young ages. The idea is that training a small child is very similar to training a puppy. Because small children have not yet developed verbal communication on an adult level, spanking advocates suggest that it is effective for small children to associate leaving a particular boundary (physical or otherwise) with immediate pain. This trains them to remain inside the boundaries even though they may not necessarily understand why at first.
Experts further suggest that if spanking is utilized and carried out correctly, it should no longer be necessary above the age of about 5, when children are not only verbally communicative, but can also understand the "why" behind rules and consequences. School-aged kids are 5 and above, therefore, other forms of punishmentshould bemore effective than corporal punishment.
Corporal punishment might also be ineffective in school because teachers and administrators do not form the kind of close loving relationships with students that parents do. Corporal punishment is most effective, again, when it is delivered in love rather than anger, is consistent, and is partnered with a follow-up conversation in which the child is left with a feeling of emotional and physical security and love, as well as an explanation. School teachers and administrators simply aren't in the best position to provide this kind of emotional follow-up.
Corporal punishment has been deemed "cruel and unusual punishment" in American public schools, and in violation of the 8th Amendment. It could be considered ineffective because it is no longer allowed. Some might argue, additionally, that this has contributed to the entitlement attitude that adults do not have the "right" to punish students physically, therefore it is not even effective as a suggested consequence to deter negative behavior.
A final argument is the fact that fewer and fewer parents are utilizing corporal punishment in the home, therefore it simply isn't a consequence that students understand or have already learned from.