<p>I’m a little surprised that your son is a math whiz and is having trouble with Spanish grammar. My son is a math whiz (in my opinion, but not his own) because he loves the logic of it and he loves the logic of grammar. It is usually one of the first things that he will master in a language, his problem is usually learning the vocabulary. This may be his own version of logic, but he has been able to use it for Spanish, Latin, Italian and Russian. Maybe if your son approaches Spanish like he approaches math, he will have better results.</p>
<p>I had to LOL when you said:</p>
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<p>After all, you live in a bilingual state.</p>