The very simple answer is that Education would finally move into the 21st Century.
Look at today's preschool children. The iPad has become their busy box. They are confused at paper magazines that do not scroll to touch. They can have relatively complex conversations and they understand pictures and icons. They are on cell phones and would soon learn to text just as they learned to speak and listen. And these children come to school in a 21st Century environment. And then, we put a pencil their hands.
There are those that think the students would not really understand unless they learned to do it for the 19th Century workplace. They make a good case for what we will have lost. But the bottom line is all the students will lose is handwriting. I propose the creation of a new discipline called something like Handwriting Arts. It would be required of all students, but not as basic to Education.
Getting back to the 19th Century, arithmetic then, was the basis of all higher mathematics. It was essential to progress. The 20th Century changed that, and in the 21st Century paper and pencil is replaced by a spreadsheet. It is easier to teach mathematics when the student is not distracted by arithmetic. Like handwriting, there would be computation courses which would stress 19th Century approaches. The emphasis, however, would be on advanced estimation rather than exact arithmetic. If I want exact information, I would use automation.
I answered the question of the negative consequences to Education without paper and pencil. Turn it around:
What would be the consequences to Education if computers were banned?
That leads to the question, what are the basics of 21st Century Education?