<p>I came to US in the midst of 7th grade and yes, I was studying Russian grammar extensively. It is harder than English, especially with different transformations of words and exceptions from rules.
However, I should mention that US schools don’t pay as much attention to grammar as any ex-USSR school would do (it even backtraces to hymnasiums before revolution of communism 
), as I have younger brother in school here. Well, not knowing what a perfect tense is in 3rd grade, grhm! isn’t exactly an idea of extensive grammar learning.</p>
<p>Study of grammar may not be so useful from first glance but it really helps learning another language and we were <em>required</em> to learn three: Russian(native for our region), Ukrainian, and English.</p>