Many of the widely-reported benefits to learning a second language appear to be the result of publication bias:
To test the accuracy of claims made about the cognitive powers of bilingual people, Angela de Bruin, Psychology Ph.D. at the University of Edinburgh, performed a meta-analysis of academic papers presented at one-hundred and sixty-nine conferences between 1999 and 2012.See also the stories in the New Yorker and NPR Radio.
Previously, a careful review of the evidence by psychologist Ellen Bialystok in 2012 firmly supported claims that bilingual individuals were more creative and better at switching between tasks (because their brains were used to switching between languages).
But because papers presented at academic conferences address in-progress research, they cover a wider spectrum of work than studies which are published. Of the conference papers de Bruin analyzed, about half provided evidence in favor of special bilingual cognition while the other half refuted such claims.
When it came time to publish, however, the numbers changed. Sixty-eight percent of studies suggesting a bilingual advantage were published in a scientific journal, compared to twenty-nine percent of those that refuted the claim.
It seems possible that there is some benefit to learning some non-English language, but what if all that time and energy were spent learning something worthwhile?
Schools are dropping cursive writing as irrelevant to the modern world, but cursive seems more useful than Chinese.