This study seems rather peculiar.

Note that they weren't asked to write about their values with respect to science. Perhaps the context increased the likelihood they did so, or perhaps there was a place dependence to the effect - the feelings of value got anchored to the location you felt them in?

Otherwise, I'd expect to see the result generalize far and wide to their lives. On the other hand, that a 15 minute writing assignment would have such far ranging effects in a person's life seems rather unlikely to me. That it would have such a wide ranging effect in that one class seems miraculous in itself.

Hence, I find it all rather peculiar.

Notice how the men did significantly worse on their exam scores after values affirmation. What's the explanation for that?

And "stereotype threat" just seems like a non sequitur here. How is that in any way related to the writing task? I see in the abstract that they found that "Benefits were strongest for women who tended to endorse the stereotype that men do better than women in physics."

And the "control" is as much an experiment as the "treatment". Why shouldn't we conclude that the "control" had a large negative effect on women, and particularly women who believed the stereotype (and data) that men are better at math?

Maybe the women who believed the data that men were better at math showed the greatest jump because they believed in data, and so had greater aptitude thereby? Maybe those women were just more impressionable to the value of others, and so disheartened by contemplating things they didn't value that other people did.

The raw data seems odd, and the interpretation even more dubious. Just peculiar all the way around. It certainly warrants further study, and I'd particularly like to see it controlled for each individual with a test of their aptitude/achievement going into the class.