Bilingual education success depends heavily upon the student's motivation.
Before my retirement, I had a student from Taiwan assigned to my Regents level Biology class (NY state college-prep level coursework).
I don't speak Mandarin or Cantonese (student's two languages) and she didn't speak English.
However, that didn't stop her from putting forth the effort needed to succeed. At the end of the year, she took the standard Regents Examination in Biology, written in a language she did not speak nine months before, and passed it outright!
As much as I'd like to think it was my pedagogical expertise, I know that the credit for her accomplishment is hers and hers alone. She put in the time and effort to learn, and she did just that.