First, some background: I’m very embedded in these sorts of issues—I’m college faculty, and I’m currently co-chairing my university’s faculty committee on academic integrity issues, where we’ve been working on tightening up policies (including making them clearer) and making sure the processes involved are clear and fair, along with the fuzzier but probably more important goal of getting a culture of academic honesty in place on campus.
So, that said, I’m with @juillet and @compmom and the others who see this as something that’s going to stick, and for good reason.
This comes down to a self-plagiarism issue involving different expectations of what is involved in that. This is to some extent understandable—self-plagiarism is one of the least-understood aspects of academic honesty in higher education among those relatively new to it, and so I’ll take a bit of space to elaborate on it.
To try to explain it, I’ll start with an obvious example. If I published a paper a few years ago in the Journal of Basketweaving Studies as (dfbdfb 2011), I would not be entitled to republish that same paper later on in the International Journal of Underwater Basketry as (dfbdfb 2014).* That would be self-plagiarism, (dfbdfb 2014) would be retracted, I would suffer professional embarrassment, and probably some other professional hit. (Not to mention that my odds of making full professor down the road would likely go down significantly, even if I otherwise meet the requirements.)
Now, reprints do happen, of course, and they’re professionally important. But if this happened—say, (dfbdfb 2011) was recognized as a really important paper in the field of Underwater Basketweaving, and so I was invited to have it republished in a collection of essays coming out this year. If the editors of the collection got my permission (and that of the Journal of Basketweaving Studies, if the publisher retained those rights), then I’d have a new publication, (dfbdfb 2015)—but it would be marked as a reprint of (dfbdfb 2011) in every case, including on anything I submitted to my university to document research productivity.
Now, to get closer to the OP’s child’s case, let’s say that I realize that (dfbdfb 2011) could be improved on, and so I write a new paper that takes some ideas from (dfbdfb 2011) and expands them in new ways. I submit this paper to Cane Weaving Quarterly, and it’s accepted to come out next year as (dfbdfb 2016)—but note that I’d be expected to cite everything that comes from my earlier paper as (dfbdfb 2011). That earlier paper is out there, and I can’t just cut and paste from it to create something new. In a very real way, (dfbdfb 2011) is no longer “mine” once it’s been accepted for publication (for the parallel with the student’s case, replace with: once it’s been submitted for a class)—it has become its own entity, and I have to treat it as such.
However, no matter what, if it turned out that (dfbdfb 2016) was essentially just (dfbdfb 2011) worded a little differently and/or with a couple new results slapped onto it, that would be self-plagiarism—perhaps not as serious a case as the (dfbdfb 2014) case described above, but still the sort of thing that could well result in a retraction, and certainly would result in very real professional embarrassment and a tarnishing of my reputation in the research community. (And really, for those of us who are academic researchers, research reputation is much of the currency—in a very real sense—we operate with.)
And that last paragraph seems to be what has happened in the OP’s case—a previous paper had been recycled, not in new and original ways, but simply by tacking more stuff onto it. This isn’t the worst of all possible cases of self-plagiarism (it’s not like the previous paper was simply turned in with a new date, after all), but it still is.
Fortunately, it’s a good learning experience, and one that will hopefully result in the OP’s child learning. That’s the ultimate goal of academic integrity policies, after all—it’s a teaching and learning process, not strictly a punitive one.
- I'm just going to go ahead and enclose my fake author-date citations in parentheses throughout to keep them together visually, even when it doesn't really work for any citation style I'm aware of.