1950/1960s
In 1958, Jack and Carl sold the American Rights to Coles Notes to Cliff Hillegas who published the books under Cliff Notes.
By 1960, Coles Notes sales peaked when baby boomers were beginning to attend high school. They had over 120 titles mostly dealing with English novels however they had numerous other subjects including math, languages, physics etc.
Read more about this topic: Carl And Jack Cole