to clarify-- students can submit a program that has been partially developed with another person, they just need to make sure the parts they write about are all created independently. that is to say, you could create 80% of the code with another person and cite that code appropriately, but the elements you describe in the written part need to be from the 20% that the student developed independently.
citations here should be in the form of inline comments, where students note which pieces of code were developed with the help of someone else (or came from an existing project) and what is newly created during the task.
hope this helps!
-brook