So the investigation says they made half of the students use Twitter to analyze a novel by posting quotes and their own reflections & commenting on tweets written by their classmates, while the others relied on traditional classroom teaching methods.

The winner is visible from a mile away, but the takeaway for me is that using the wrong tool for the job is stupid, not that Twitter itself makes you dumb.

You seem to suggest you think that Twitter is the right tool for some job. Using it had, manifestly, the observed effect, regardless of what other tool might or might not be deployed elsewhere. Using another tool simultaneously enabled quantifying that effect.