In one book, it is said the founder (Mr. Toru Kumon) made a sensation among the students for allowing them to use "cheat books," books with answer keys and worked out solutions.
In another written by one of his sons, Hiroshi Kumon, the author said that his father let him use his older brother's books to see how some problems were solved.
Well, well, well ... "Example isn't another way to teach, it is the only way to teach." - Albert Einstein
See that philosophy in action at our web site English3day.