Is it obligatory when studying to intend to benefit from it and not merely to get good grades, otherwise one would be cheating?

This statement, in its absolute form, is incorrect. A distinction must be made between the sciences of Sharia (definition) and worldly sciences. It is not permissible to seek knowledge of the Sharia solely for grades; rather, one must purify their intention for Allah in seeking it. As for purely worldly sciences, it is permissible for a student to study for the purpose of achieving grades. However, there is no reward for this unless one intends thereby to serve Islam and benefit Muslims, or to fulfill a communal obligation (fard kifaya).