I constantly remind him how much Mommy loves him and wants him to be good in school. I explained to him that since my talking to him and his teachers giving him time-outs haven't worked, from now on, when he gets a bad report, he will get the belt. He agreed that this will definitely work, but I hate using the belt and consider it a last resort. What do you think?
At home, you find him to be a delightful boy who exhibits none of the negative behaviors he demonstrates in school. And now he has, in essence, said to you, "Yes, Mommy, hit me with the belt if I don't behave in school." So, at least for the moment he is telling you that you need to take control of the situation in school by threatening him with a whipping. This tells me that he doesn't believe that his teacher and the other adults in the school can keep him under control. He's scared and it's coming out in negative, sometimes anti-social, behavior.
Please ask the school counselor to observe him in class and to begin counseling sessions with him. It may be worthwhile to have your son see a family therapist or child therapist a few times. Perhaps there are things troubling your son that he has not been able to share with you -- issues that hinder his ability to focus in school and cause him to act out inappropriately.
Your son may also benefit from a CORE evaluation, which is a comprehensive evaluation guaranteed by federal and state law to determine the nature of a student's problems and how to address them. In any event, the threat of the belt, even if it works, is not the answer. Your little guy should not feel like he deserves to be hit because he can't behave as he should in school. There are underlying causes for his misbehavior. If this has been happening throughout the entire school year, the school personnel should have tried different approaches and counseling should have begun long ago. If it's recent behavior, there may be reasons for it that need to be uncovered in a calm, understanding, non-blaming manner.
Let's get this little fellow some help. He can't be expected to figure out his behavior and correct it all by himself.