"I am a middle school student from today."
Translation:나는 오늘부터 중학생입니다.
Like with English, by placing the time adverbial at the start of the sentence, the emphasis is put on the time factor. So,
오늘부터 나는(/저는) 중학생입니다 = From today, I am a middle school student.
Its neutral position (no emphasis) is as shown in the example, at the end of the sentence i.e.
나는(/저는) 오늘부터 중학생입니다 I am a middle school student from today.
저 (self-deprecating/humble " I ") is used to show respect to Listener(s). So it tends to get used in more traditional communities which still preserve some kind of hierarchy e.g. in Big Corps.; public/religious institutions; schools; stores; when addressing the elderly or people with status(officials); etc.
나 (not less polite) tends to bring speaker-listener(s) on a more equal footing. (Probably closer to the " I " in English) So it tends to get used in more liberal-minded communities s.a. new start-ups; adult-eds; etc.
There is no clear dividing line especially now that Korea is evolving into a more liberal society.
But it's worth noting that
• on first encounter, use 저; then build up from there as relationship is fully established. 나 is viewed as associating too much importance to yourself.
• an overuse of 저 could be seen as 'lack of self-confidence' or even 'satire'. Overuse of 나 could be viewed as 'boastful', 'arrogant' etc.
• drop subject when unsure and use verb endings to show respect, politeness etc. if needed.
Really bad English. The sentences "I am a student from the past" or "from the future" are legitimate and mean that the student traveled in time. But "from today" or "from now" do not make sense with this approach (no time travel involved). "From now ON" has a different meaning - equivalent to "starting now". I guess one could say "from today on", it seems grammatically ok but I don't think I ever heard anyone say it.
And then, as if a non-sensical English phrase was not enough, the Korean phrase mixes honorifics.
Please remove this exercise!