Was there ever a grade 13 14 or even up to grade 20 in schools?

No. In the US, in the 1800s and early 1900s, very few people went past the 8th grade. Only the children of the wealthy elite went through grade 12. They were preparing for university work, which is why the schools were often called "prep schools". 

im sure you must know that or  you need to go back to school and learn 

not in American public schools, no

No, that would be college.