is a native speaker and speaks to the kids exclusively in their native language. I have a colleague whose Italian wife speaks to their kids only in Italian and it's really impressive to see the kids (who are 2 and 4) switch between Italian and English when talking to their parents (properly identifying which language to speak with which parent).

Very much anecdotally, I've observed it's less successful where one parent tries to speak to kids exclusively in a language they acquired later in life.

My wife will only speak to our daughter in Japanese. And she will only respond to my daughter if my daughter speaks to her in Japanese.

Daughter (7) is completely bilingual.

Writing is a different story. She knows her Japanese characters, but written Japanese also uses a lot of Chinese characters. My daughter does not know these as well as a 7 year old in school in Japan does.

They not only can't read or write the language, but also often have trouble passing professional speaking tests if they haven't complemented the home speaking practice with formal study.

They are 100% fluent conversationally (Germans recognize their Munich accents) but would have difficulty with things like literary analysis in German because they don’t have the cultural background like a native German with German parents. They do all read and write very well, though.

I would estimate that 60% of my students are fully bilingual. Another 20 % are at least trilingual (2 non-English native parents, plus education in English). G16’s best friend is native proficient in English, Turkish, and German, and proficient in Mandarin. I have another student that is Turkish, Hungarian, English, and German fluent. English-Spanish-German. The list goes on. My students amaze me every day. But the key to that is mother tongue development. Additional languages are easily acquired if mother tongue skills are good.

and lots of language study, it's that people toss the word "fluent" around much too freely. People seem to think being able to generally understand a news broadcast or a newspaper article connotes fluency.

And you're exactly right about having true fluency in a native language. It's nearly impossible to learn another language properly without a full grasp on grammar and syntax in your native language.

I have taught students who have no native language skills because their non-native speaking parents spoke only English to them as they grew up. It’s disastrous. Our EAL staff insists that parents speak their own language to their children—we can teach them English. Any pedagogical study will show that this produces the best outcomes.

because I don't know any of the science. But I have many friends who are excellent linguists and many friends married to people for whom English is a second language. I've observed the kids of the latter do much better with language acquisition in both English and the other language than the kids of the former.

I'm deeply sad that my wife didn't see it as such. One of my few deep regrets of my marriage and thus far brief experience in fatherhood has been my inability to convince her to use her native language with our son.

I know it's never too late, but that he now protests any time I try to read to him in her language with "don't use those words. Use the other words!" and shows no understanding of the language at all is incredibly dispiriting.

in the job market. As is dual citizenship. The kids who speak French are also French Citizens. My kids have Irish citizenship through their grandparents. All have EU passports, as well as US passports.