How should disallowed collaboration on a freshman homework set be handled by a TA? I'm a TA for a freshman calculus class, and I've just finished grading the first homework set.

It's fairly clear that there has been some collaboration going on, which is disallowed in my institution. For instance, a pair of students both put exactly the same (very) incorrect solution to a trig problem, and a group of four whose work is next to each other in the pile (i.e. they sat near each other in recitation) have all made the same (more common) errors.

The course started last week and this was the students' first ever assignment: it was set on the second day of class and due on the fourth day of class.

I'm aware of what I "should" do, i.e. report it to the instructor and let him follow the necessary disciplinary procedures. But is this necessarily the right course of action? It would probably be just as beneficial to these kids' academic integrity in the long run to tell them I'm onto them and never to do it again, as it would be to have them officially disciplined. It's likely that many of these people (should but) don't know the policy on collaboration.

Advice would be greatly appreciated.
I personally follow the rule "once is nothing, twice is a habit". I think a warning would be a good way to start. I do, however, think that it is still a good idea to run this by the instructor. I assume he/she is responsible for the course and the decision is up to him/her. You can explain your point of view and perhaps get some feedback on the matter. In addition, by taking up the discussion the problem is in th eopen and it makes it easier to catch repeat offenders. If you keep it secret, the culprits, in the worst case, can get by repeated cheating for each new teacher they encounter.

Cheating is an abomination but I think people are allowed to make mistakes. I also think most people learn from mistakes and will not easily do it again. But, it is necessary to make sure they understand their attempt has put them under scrutiny, that is probably "punishment" enough.