To say the bible doesn't teach spanking is error. It does say use a rod which was a switch like thing that would be flexable causing pain but not injury. I use the belt, left welts a few times, ain't gonna kill em.
Proverbs 23:14 (Whole Chapter)
Thou shalt beat him with the rod, and shalt deliver his soul from hell
Proverbs 23:13 (Whole Chapter)
Withhold not correction from the child: for if thou beatest him with the rod, he shall not die
30The blueness of a wound cleanseth away evil: so do stripes the inward parts of the belly.