In this first set (originally titled simply "Bob Books"), the stories start out very easy (words like Bob, Sam, sat, etc.) and very gradually increase in difficulty. All letters are introduced except "Q" and the stories are made up almost entirely of three-letter-words. We found the pace and order in which new words were introduced to be very helpful. We have used the Bob Books to teach two of our children to read. They were both interested in learning to read when they were four years old. After they had worked a bit on learning the basic sounds of the alphabet, we found this first set to be an easy and rewarding practice for little eager readers. My daughter started this set at age four and finished it early in her Kindergarten year. My son started the set at about the same age, but took a little longer to complete it. Although I try to encourage my children to finish what they start (which generally means finishing a small book at one sitting), there are times when things go much more smoothly when I learned to follow the pace that was appropriate to their needs.