There are a handful of students that complete regular flight courses over the summer...normally less than 15 (from my observations). Its a good way to catch up if you are 'behind' due to CODO (transfer into the program) or if you want to get ahead in your ratings.

Personally, the 15 hour XC requirement is better done on your own time and own dime...it will provide MUCH more flexibility than Purdue's course in terms of places you can go. It'll also provide much more confidence and experience for the students to do it this way, as Purdue's strong safety culture places massive restrictions on solo operations that (IMO) do little to foster individual ADM development that would naturally occur with experience and a little mentoring.