The public schools achievement tests scores speak for themselves. Seventy five percent of students using text books require more to retain the material. In this manner they can teach from text books to 30 to 50 children at a time. Not all children will learn a subject to the same degree in 180 hours. Some need much more, some need much less.
Some children can learn the material twice as fast using a different method.
Instead of measuring 180 hours we should be measuring the end result. There are many, many more effective ways to teach about God s world. The WholeHearted Child Home Education Handbook by Clay Clarkson and Sally Clarkson. Home schoolers have the advantage of choosing the curriculum that suits their child. They can use a variety of approaches and a variety of levels if necessary.