If true, this study is yet another great reason for learning other languages.
Low intelligence or inability to excel in other subjects at school is not indicative of ability to learn a second (or third or fourth) language. Statistically speaking, almost anyone has the capability to learn multiple languages.
Now the province of New Brunswick needs to learn that research by linguists, neural scientists, and educators all show that the earlier the better for learning new languages. Your body actually begins to re-direct those parts of your brain used for language development to other tasks once you hit the teen years. To be successful, immersion needs to start in kindergarten for all NB students in both official languages. Grade 5 is too late!