I couldn`t find anywhere ER diagram for High School... can you help me?

First its not a good idea to piggyback your question on someone else's. This can lead to confusion. You should start a new thread. So I've moved your question to its own thread.

This site:
Library of Free Data Models from DatabaseAnswers.org (http://www.databaseanswers.org/data_models/)

Has a large collection of database models.

Thank you so much;)