A Christian youth is not ready for the duties of manhood or womanhood until he or she knows how to abide in Christ day by day. The 3 Rs and all that comes after is a vital part of discipleship. Our children should excel in all the subject areas that are taught in other schools. They should have more, though. That is a truly Christian education.
Life skills training.
Taking dominion means having a hands-on acquaintance with God's creation and being able to utilize and even improve the tools of culture that other men have developed. God's creation is not only very useful, it is also very beautiful. Enjoying that beauty and re-creating things of beauty is a vital part of what it means to be made in the image of God. Our children are only fully trained when they have learned to both appreciate and incorporate beauty in their everyday lives. So our vision of what it takes to pass from being a youth to being an adult is rather all-encompassing and makes the mere passing of an academic hurdle rather inconsequential by comparison.