How can I repeat parent table field only once for a group of child table fields?
The only way I can think of doing this without custom coding is by using the Views Field View where you create two different Views Displays, one with the contextual filter, save them both, then "embed" the contextual one into the other view. 

This type of database query can be very performance intense, and caching is recommended. Or avoid it if you can. 

In your case you can keep your original accounts view, but remove the student fields. Add another Display (Block) that is showing student name gender and age, and add a contextual filter for the account, save the view. Then in your original views display add the field for the student info. 

You may need to adjust how the labels are shown, so you don't have them duplicate/in odd places because of the recursion.