The fundamental result that Dr. Seuss has made to American Literature is the idea that a child's viewpoint on life might not necessarily be easily dismissed. The very idea that adults can consider giving "Oh, the Places You'll Go" to someone who has enjoyed a promotion or to someone in a new phase of life would prove that his contribution to American Literature is quite significant. The belief that within children's literature much is present to reflect truths about life and consciousness is where Dr. Seuss has made his greatest contribution, his largest impact. In he final analysis, the transformation of children's literature from what is to what can be represents his largest contribution.
One could easily argue that the Dr. Seuss series has instilled in elementary-aged schoolchildren a desire to read, since the series has been so popular for so long. It also helps those students with basic language fluency and storytelling skills, where most literature is more advanced and less accessible to that age group.
Add to that the fact that it is so much a part of American popular culture and has been for decades. Generations of readers have now been raised on these stories, their parents having read it to them, and now they are reading Dr. Seuss to their children.
Lastly, consider the heavy use of illustration, alliteration and rhyme in these books, introducing children to literary concepts at a young age, without them even realizing it.
True, the alliteration, rhyme, and other aspects which are key in all of Dr. Seuss's stories expose the very young to important literary elements. Seuss's works are also an unparalleled source for primary teachers to use in forming a foundation for these and many other literature/language skills in elementary classrooms.
Theodor Geisel was definitely a pioneer in raising the awareness of the general public to the value of children's literature. His books, as well as many written in years prior to his success and for generations afterward are "living" proof that kiddie lit is an incomparable force in World literature. Thanks, in some measure to television and movies.
However, although Ted Geisel's books were written and published for children, except Oh the Places You'll Go, both the humor and the societal commentary in all of his works appeal to "children" of all ages.
Books by Dr Suess were designed to appeal directly to children through the use of humour, ryhme and bright pictures that can be 'read' even by the non-reading children.
Dr Suess has created a revolution in reading and has impacted the worlds literature for many years in the past and many years to come.