Jesus is Lord of all things. There is no division between the sacred and the secular. God is the source of all truth. God's Word is the ultimate in revealed wisdom, and all human experience must be subjected to it.
I agree with all of these. So why do I so often find myself squirming when I look at curricula that take these ideas seriously, and purport to relate all of learning to God and His Word? Is the problem with them, or with me?
Let me try it from another angle. The Bible says we are to eat and drink to the glory of God. Jesus also instituted the Lord's Supper, ennobling the act of eating to become a way in which we have fellowship with God. Now, suppose that devout theologian combined these two truths and taught that every meal should be the Lord's Supper. Every child sitting down with a peanut-butter-and-jelly sandwich must comport himself as if he was partaking of the bread and the cup. Every time we ate strawberry ice cream, we should meditate on Christ's sacrifice as symbolized by the red of the strawberries.
This new practical theologian would be taking things a little too far. And in his zeal, I think he would be undermining the Lord's Supper. It does take us from the human need for physical nourishment to the human need for divine nourishment. But if it were not a special and sacred occasion, if it were simply our ordinary meals, we would cease to see it as a vehicle to Christ and start to treat it as simply a way to get full. (Seems like the Corinthians might have had a similar problem.)
Similarly, if we get too carried away with insisting that every scrap of human knowledge must be extracted from, tied to, or analogized with Scripture, we run the risk of treating the Bible as simply a vehicle to the knowledge we need to function, and not as it was primarily intended, a means to reveal God himself to us.
I have also seen this ideal carried into dishonesty. For instance, a teacher script for introducing the alphabet I saw once had the teacher essentially instructing the children that God had created capital letters. Now, even if I had assurance that writing was a matter of direct divine revelation, I would be a bit perplexed as to why God only revealed the truth about capital letters in the last millenium to the scribes of a handful of alphabets.
Worse yet is the area of history, where it is far too easy to turn every twist and turn of events into an illustration of this or that Biblical principle, ultimately leading us to the conclusion that if we're doing fairly well (and if we can afford all these books, we probably are), God must be on our side. Presumption, pride and dishonesty are not honoring to God, however much lip-service they may pay to him.
Besides, if there really is no distinction between the sacred and the secular, then we have no need to convert every topic by pasting a Bible verse on top of it. If everything has been created by God, then that in itself is reason enough to study it. I think we will find more and more of God's character as we delve deeper and deeper into whatever we study--but the connections are often subtle and hard to tack onto a third-grade text.
This is not to say that we shouldn't hold all learning accountable to God's Word, and reject anything that contradicts it. Or that we should relegate Bible to a distinct study and keep it out of all our other subjects. It's right and proper to make God the focus of all our life. But seeing God reveal himself through all his world needs to come naturally, not be forced to increase the "spiritual" appearance of our schoolbooks.