"A school is a place."
I think it you could perhaps say that if you had a specific school in mind(?), but generally it would be more natural to use the topic marker than the subject marker for general "X is Y" statements.
I wrote 학교가 instead of 학교는 and didn't work. I kind of get why it didn't work, and I'm ok with the correction of writing it as 학교는 and not 학교가, but then they asked me to translate "학교가 장소입니다" from Korean to English. Is this a bug? Maybe I wrote right the first time, I don't know...
Both are grammatically correct because context is unknown.
Really, I need to revisit Baaics1 and 2 tips. I recall that the difference was explained how the 은 / 는 has ideas like x is the answer, x is the one out of many choices, and x is regardless of others...or something like that.