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.
Study of grammar may not be so useful from first glance but it really helps learning another language and we were _required_ to learn three: Russian(native for our region), Ukrainian, and English.