Most systems are bias because it does not take homeschooling into consideration.

ie.

Emotional abuse. Emotional child abuse means injuring a child's self-esteem or emotional well-being. It includes verbal and emotional assault — such as continually belittling or berating a child — as well as isolating, ignoring or rejecting a child.
Medical abuse. Medical child abuse occurs when someone gives false information about illness in a child that requires medical attention, putting the child at risk of injury and unnecessary medical care.
Neglect. Child neglect is failure to provide adequate food, clothing, shelter, clean living conditions, affection, supervision, education, or dental or medical care.
In many cases, child abuse is done by someone the child knows and trusts — often a parent or other relative. If you suspect child abuse, report the abuse to the proper authorities. Reference Link

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Signs of Neglect
Frequently absent from school
Theft of food or money
Consistently poor hygiene
Lack of appropriate clothing for weather or season
Frequently unsupervised, left alone or allowed to play in unsafe situations and environments
Lacks needed medical or dental care Reference

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Physically, pain tolerance is different in everyone. Bruising can be on the bone and sometimes not show. Fractures and broken bones as well.

Personally think for most kids spanking is a form of abuse especially if you are being spanked/hit from an adult in anger. Meaning if the adult is just angry, the easiest emotion to grab they often are in fight or flight and them spanking you is a reaction not a form of 'punishment' or guidence.

Who here has learned a lesson from being hit?

For anyone raised biblically try out some historical research on sheep rod/staff and talk to a shepard.