When a classmate fills out everything in their profile, it usually fills up the entire screen so the user does not see the box for sending a private message unless he/she scrolls all the way to the bottom of the profile. This is particularly true when a classmate uploads a bunch of photos to their profile.

The admin does not seem to have the ability to reorder the page to put the private-message-send up at the top (if it were at the top, it would be more obvious that you can send private messages). I suggest enabling a site admin to place a link at the top of the page that says "Send this classmate a private message" (or whatever) and when the user clicks on the link it takes him/her straight to the bottom of their classmate's profile (so they can send them a private message).

The scenario I'm mostly concerned with is where a user sees a classmate profile and would like to send a private message -- but is not aware they need to scroll down to the bottom of the profile.

Your suggestion is valid and will be considered for future updates to that page.