It probably wouldn't be too much to say that, as a family, the Schaeffers were the most influential Christians of the 20th century. Francis, the philosopher-theologian; Edith, the spiritually disciplined matriarch; Franky, the literati rebel; and Susan Macaulay née Schaeffer, the homeschool pioneer, theorist and apologist. Susan's book For the Children's Sake remains one of the standards of the modern homeschool movement, and continues to influence parents, writers and educators with its Christian common sense approach to home teaching.
Macaulay's own homeschool experience began when she discovered the writings of Charlotte Mason. A 19th century English schoolteacher, Mason thought children should be taught according to their abilities out of "living books," not as classroom units out of standardized textbooks. Part of this is to encourage love of learning, but even more fundamentally it is meant to keep kids from boredom—while some dour souls may view only drudgery as worthwhile, Mason saw that keeping kids interested was essential to teaching them.
But this doesn't mean children are to have free reign or that they ought to form their own curriculum. Authority is needed, but the right kind of authority, the kind that also offers enough freedom for young minds to develop and engage the world around them. Education is a discipline, and as such requires boundaries, though the very word "boundary" suggests latitude between the lines. Because character development is one of the chief ends of education, the boundaries must reflect this, offering children a place to become good productive people.
This is some of the philosophy espoused by Macaulay (much of it taken straight from Mason). True education, she suggests, is a "science of relationships" in which children are taught their relationship to God, to their parents, to themselves, and to the rest of the world. While a lot of schools focus on cramming information, names and dates, propaganda, etc. down kids' throats, the teacher's true calling is much more broad and at the same time much less so, as it is virtue and morality she ought to be encouraging in her pupils.
The homeschool curriculum must reflect this. While there are different opinions as to the validity of the Charlotte Mason method, Christian homeschool parents are united on this point—and Macaulay's book was one of the first to bring them together. Already a classic (it was first published in 1984), For the Children's Sake is an appeal to make home education not about parental ease or the impartation of facts, but about the parental sacrifice needed to raise children ready, willing and capable of living God-centered lives in whatever circumstances they find themselves.