"Seit wann bauen Sie diese Schule?"
"Wir bauen seit einem Jahr an dieser Schule."
The answer does not match to the question. The questions asks about the complete creation of a new school that has not been exists before whearat the answer points out that the school already exists before and is not created new.
So there are two cases of possible - and differnt - conversations:
Correct case 1
"Seit wann bauen Sie diese Schule?"
"Wir bauen seit einem Jahr diese Schule."
The conversation belongs to the creation process of a new school that has not been exists before.
Correct case 2
"Seit wann bauen Sie an dieser Schule?"
"Wir bauen seit einem Jahr an dieser Schule."
The conversation belongs not on the creation process of a new school! It belongs to a build process on an School that has already exists before but needs a process of repair or enhancement.
Intelligent and creative answering / hearing
In the optimization of conversations its sometime used to repeat the question in the answer itself by 100%, to let the person who asks know that you fully understand the question, highlight the core of the question with your words, affirm clearness and pretent a sentence that can be cited in publishments (like newspaper/literature) to third persons.
Where is the intelligent hearing? The difference between the question and the answer might be a correction of the question itself. Whearat the question asks about the creation of a new school does the answer points out that the school is not created new and has already exists in the past and only an enhancement or repair process is in work.
an
not come at the end of the sentence?