A potential objection to the insistence on Christian education is that Moses and Daniel received an unbelieving education in their day. Therefore, one may argue that it is acceptable to send Christian children to secular schools today (i.e. American public schools). But what does the Bible actually say about Moses' and Daniel's education?
Interestingly, the book of Exodus says nothing about Moses’ schooling. In fact, the only passage that mention's Moses' schooling is from the New Testament, namely Stephen’s speech before he was stoned to death in Acts 7:22:
And Moses was instructed in all the wisdom of the Egyptians, and he was mighty in his words and deeds.
While Stephen received this information from tradition and not from the Old Testament, there is no good reason to question its veracity. Assuming an early dating of the exodus, Moses was born in 1526 B.C. He was nursed by his mother, and then “when the child grew older” he was given to Pharaoh’s daughter and “became her son” (Exodus 2:10). Belonging to Pharaoh’s daughter, it makes sense that Moses was instructed in the wisdom of the Egyptians. This probably refers to Egyptian language, literature, and customs. However, there is not enough information to determine the age of when this instruction took place. We only know from Exodus 2:10 that Moses was not a young child.
Daniel’s case is more interesting. Daniel and his three friends (Shadrach, Meshach, and Abednego) were taken into Babylonian captivity in the 6th century B.C. The book of Daniel tells us that he and his three friends were selected by the king to be “educated for three years” by the Babylonians (Daniel 1:5), where they would learn “the literature and language of the Chaldeans” (another name for the Babylonians) (1:4). Here is Daniel 1:3-5:
3 Then the king commanded Ashpenaz, his chief eunuch, to bring some of the people of Israel, both of the royal family and of the nobility, 4 youths without blemish, of good appearance and skillful in all wisdom, endowed with knowledge, understanding learning, and competent to stand in the king's palace, and to teach them the literature and language of the Chaldeans. 5 The king assigned them a daily portion of the food that the king ate, and of the wine that he drank. They were to be educated for three years, and at the end of that time they were to stand before the king.
It must be noted here that Daniel and his friends were already “youths” who were “skillful in all wisdom, endowed with knowledge, understanding learning, and competent” (v. 4). Though their exact age is not clear, these were Jewish youths who had already received an Israelite education.
Can Christians Receive a Pagan Education?
So yes, Moses and Daniel studied subjects under "pagan" teachers. This makes the point that it is not wrong for Christians to study subjects under unbelievers and at unbelieving institutions. However, this still leaves the question as to what is an appropriate age for studying under unbelievers. There is no indication that Moses or Daniel were young children who were trained in a pagan worldview from age 5 to 18, as in the case in modern American public schools. Moses’ age when he studied under the Egyptians is unclear, but he is said to have been an older child (Exodus 2:10). Daniel was probably a young man, as he was already “skillful in all wisdom, endowed with knowledge, understanding learning” when he undertook his Babylonian studies (Daniel 1:4).
Furthermore, Moses and Daniel were both in unique circumstances. Moses lived when the Israelites were under Egyptian slavery, and he was given to Pharaoh’s daughter so that he would not be killed (Exodus 2:3). Daniel lived when the Israelites were under Babylonian captivity, and he was chosen by the king for studies. Neither of these were entirely voluntary cases. Barring some exceptions, Christians today are not under slavery or captivity, nor are we having to send children away to avoid being killed. We may not be in the new heavens and earth yet, but we have freedom to live as Christians and give our children a Christian education.
That being said, Daniel’s situation may serve as an example of how mature Christians can attend non-Christian schools. Once Christians have received a Christian education in their childhood and have reached maturity, they may be in a place where they can attend secular universities and professional schools. (Of course, there are serious problems with modern universities that should give Christians pause. Every case is different, and a particular school environment and an individual's maturity should be taken into account.)
Knowledge is not limited to Christians. There are certainly many skills and much information that we can learn from unbelievers—languages, skilled labor, music, etc. I myself read economics and history from unbelievers quite often. As mature Christians, we should be able to filter things through a biblical worldview. Now some adult Christians still struggle with this, whether it be psychology, law, or politics. But what seems apparent is that children are unable to filter through unbiblical teachings (nor should they be expected to). Children need grounding in the Christian worldview before they take on such a difficult task.