Legal paper trail
Like hospitals, informed consent is required for many procedures in schools. Primary and Secondary schools have legal obligations for the minors who are entrusted to their care during the school day. Signatures from parents and guardians on paper documents provide a reasonable record that consents have been informed and permissions have been granted.
Students transferring from one school to another require a written transcript. Often this is signed by one or two people in authority who are responsible for the accuracy of the document and could be contacted for verification.
Paper is incredibly easy to use. Make marks on it and as long as the content is readable, almost everyone can use it.
What you see is what you get with paper. Electronic solutions often have to deal with a variety of different viewing devices.
Students taking notes and performing exercises may perform faster with pen/pencil and paper than electronics especially when the work involves producing written equations or diagrams.
The act of writing can reinforce what is being learned. Processing what is heard or seen into writing helps students to remember the content.
Paper is an important medium for art and it can have more applications beyond being a surface for the artwork. It can be transformed with cuts, folds and layers to produce three dimensional work.
Paper requires a low investment. Technology, especially software development requires a larger start up investment of both time and money. Even though students, staff and parents are usually technology literate, there is an adoption curve to be overcome with any new technology.