He's 4 and he can be naughty at times, but today he's gone too far, he's been spitting at the school windows and he's also scratched a boys face as he wanted the toy the other boy was playing with 
Im so upset with his behavior, we do discipline him by taking away toys/treats and we talk to him about what is not acceptable.
I just don't know what else to do, I feel I'm failing as a parent.