"There are few students in this school."
Translation:В этой школе мало учеников.
Yes, "a few" and "few" have slightly different meanings. It's explained well here: http://english.stackexchange.com/questions/1866/a-few-vs-few
The difference is similar in Russian. Also несколько would probably be even better translated as "several"
That is possible, though obvious. Студенты do not study at school, so they should not be there in great amounts.
How come "студенты не учатся в школе"? If there is no context, I can think of a "высшая школа", not necessarily a "начальная или средная школа"
I've reported this. I agree that "мало студентов" should be an accepted solution, given the fact that the sentence lacks context, and the words "students" covers both "студенты" and "ученики".
It is a school with university rank, for example the "Высшая школа экономики" in Russia (maybe I am too subtle with this, as while the term "school" is a generic one, it is usually used for the elementary grade of education)
Высшая школа экономики is a university, not a school. When referring to an educational institution, школа is not a generic term: it only refers to where schoolkids go.
Unless it is used as a part of the institution's name, of course. ВШЭ is as much of a school as a guinea pig is a pig. Names are sometimes deceiving. For example, Moscow State Linguistic University is, arguably, not a linguistic university—at least, not primarily (linguistics is not what it is or historically was focused on) but rather a language university, i.e. the one that teaches translators, interpreters and language teachers (and also linguists, lawyers, psychologists).
There is, however, one context where this truly works: when a "school" is not your average school for children but a company that provides classes that teach certain skills (e.g. "animation school", "fencing school"). Using ученик in this case is odd.