In math in English, the teacher does not translate concepts.
Students learn fractions directly —they do not learn
"fracciones" and then its translation. That is immersion.
This distinction seems minor but is the difference between someone
who speaks English and someone who mentally
translates from Spanish to English. The first is fluency;
the second always shows.
That is why we start at age 3. Before age 7, the brain acquires
languages without conscious effort. After 7, every new language
passes through filters of the native language. The difference is
permanent.