It depends on why he tattles.
- To get other people in trouble? (He’ll tattle on people you punish, and want to see them “get theirs”.)
- To get some feeling of superiority? (He’ll tell many people, and he’ll have a low view of the rule-breakers.)
- To relieve anxiety over rules being broken? (He’ll seem mostly concerned that something bad is going to happen because the rule is broken.)
He may have all of these reasons, or even other reasons, but each reason has a different remedy.
Case #1 is probably the most common and the most perplexing, because of course you put your rules and your consequences in for a reason. Siblings can provoke each other into rule-breaking as part of their little wars, and will cut off their noses to spite their faces. You are stuck being Solomon. Take Solomon’s lead, look deeply into the situation, and use your imagination when coming up with consequences.
Case #2 is obnoxious, even if he only gossips to you. You need to teach him to be discrete, kind, and as charitable as he can when he needs to report someone else, and it is OK to impose consequences when he doesn’t.
Case #3 requires helping him think through the weighing of the harm done by failing to report vs. the harm done to his relationships by reporting. This is something you can talk to his teacher about, but remind him that the Church has private confession because it is sometimes more charitable to ignore the faults and offenses of others. He might be taught the mercy in overlooking the offenses of others. If he has a “greater rule” arguing in favor of not reporting a clear wrong, that might lower his anxiety.
For an 8 year old, I’d say that if he is constantly concerned about other people failing to do what they ought to all of the time, he’s never going to have any peace. People make mistakes, and he needs to learn to expect it and love them, anyway. Correct only when a) he has to and b) correcting them in this case is his job. This the idea (for you, not your 8 year old–you need to translate!).
One of the first things to learn if you want to be a contemplative is how to mind your own business. Nothing is more suspicious, in a man who seems holy, than an impatient desire to reform other men. A serious obstacle to recollection is the mania for directing those you have not been appointed to direct, reforming those you have not been asked to reform, correcting those over whom you have no jurisdiction. How can you do these things and keep your mind at rest? Renounce this futile concern with other men’s affairs! Pay as little attention as you can to the faults of other people, and none at all to their natural defects and eccentricities. --Thomas Merton, New Seeds of Contemplation
As Xantippe suggested, it is good to ask “what good will come from it if I tell or correct?”