What is the ruling on money taken from students in exchange for private lessons, and the salary for teaching in a private school that forces teachers to give high grades to students, and how can this earning be made lawful?

Private lessons are permissible as long as they do not involve unlawful seclusion (khalwa) or temptation (fitna), and provided that the teacher does not favor their students in grades over others, and that it does not compromise their primary work. As for giving students more grades than they deserve, this is forbidden deception and injustice. It is obligatory to refrain from such actions and to repent for what has occurred. There is no harm in benefiting from the payment for private lessons and the school salary.