Altar serving in a state of mortal sin

[ConstantineTG]

I hate to drag this out so long (it’s probably my scruples), but is there a church teaching on this?

How about this, if you’re going to serve on the altar, ask the priest. If he lets you serve, then serve. If not, then don’t. Or better yet, confess to that same priest and get it over with. If you are not sure if its mortal or not, confess it anyway. We can confess venial sins.

To directly answer your question, the only teaching is that we cannot receive if we are in a state of mortal sin. Altar servers are not required to receive during Mass, no one except the celebrant is required to receive during Mass. That is why the priest must be free from mortal sin because he is receiving Communion. That is the Church teaching.