Preteens and teens may appear dazzlingly fluent, flitting among social-media sites, uploading selfies and texting friends. But they’re often clueless about evaluating the accuracy and trustworthiness of what they find.

Some 82% of middle-schoolers couldn’t distinguish between an ad labeled “sponsored content” and a real news story on a website, according to a Stanford University study of 7,804 students from middle school through college. The study, set for release Tuesday, is the biggest so far on how teens evaluate information they find online. Many students judged the credibility of newsy tweets based on how much detail they contained or whether a large photo was attached, rather than on the source.”

Stephen