Custom database tables, no.
WP has custom post types https://codex.wordpress.org/Function_Reference/register_post_type. Courses, Teachers, Parents and Students would all fit nicely into custom post type. Or even Courses and “People” where People has a custom taxonomy https://codex.wordpress.org/Function_Reference/register_taxonomy to divide them into teachers, parents and students. I don’t know how much experience you have with WP, but it’s easier to work within the system it presents then to try to bend it into something else. Using custom post types and custom taxonomies you can then create the relationships that that you’re looking for.
