If you would like an order to show up under a particular Student Account, you will need to connect the email of the Purchaser to the email of the student in People by adding a Relationship between the two. Click on the student's name in People, select the icon Edit this Contact, and scroll to the bottom to add the Relationship.

If the person has two email addresses, you could make a Custom Field for your Product such as “Secondary Email Address” and select Field Type Email. This way no matter which email address the purchaser uses to purchase a Product, both are attached to the same person.