To learn about God?
To worship together as a “school family”?
To give the kids an opportunity to “lead worship”?
Perhaps the reason is more educational. Just as the disciples asked Jesus to teach them to pray and as parents in the Old Testament were commanded to instruct their children, so also a Lutheran school should teach the children in its care to pray. We are all by nature Enthusiasts who left to our own devices will “give” God our filthy rags of self-centered instrumental selections, vocal stylings, puppet performances, or chancel dramas. While children are in school to learn skills and gain knowledge they will need to function as mature human beings in the world, a Lutheran school should also teach children how and why Lutherans pray.
“However, ceremonies should be celebrated to teach people Scripture, that those admonished by the Word my conceive faith and godly fear, and may also pray. (This is the intent of ceremonies.)” --Apology of the