- Sending an email is dependent on the contact objects, So I would suggest you make use of contact objects for students instead of a making new objects. - If you want to make use of student custom objects only then to send an email student should be associated with the contact and the email will be sent to the email address of the contact. - I will recommend you to go with the first pointer, for desired results.
@Creativesoul Are you looking to send marketing emails to the students? If so, they would need to be contacts and custom objects. currently, there isn't an ability to send marketing emails to any other object apart from contacts.