Would the conversation with the two sentences be like this? Aさん：プールはどこですか？　Where is the pool? Bさん：プールは学校です。 or プールは学校にあります 。 If so, both of the meanings are almost the same as AKIさん mentioned. "プールは学校にあります 。” There is the pool in the school. ある/あります are often translated as "There is". "existed", etc. I think that プールは学校です is a shortened form of プールは学校にあります 。in this case. プールは学校です。is just like Bさん pointed out a school and said, "学校". Bさん omitted "にあります" and added "です" in this case, then プールは学校です sounds primitive and odd, but Aさん can understand the meaning. *は is called 副助詞, the 「は」 topic particle, topic marking particle, or etc. は identifies a topic, プール is the topic, in this case. は is often translated as "is".

プールは学校にあります。= The swimming pool is in a school. プールは学校です。 = The swimming pool is a school. So I think you can understand those sentences are totally different. I guess, you are confused like “はさみはつくえのうえにあります。” and “はさみはつくえのうえです。” is that correct? If you are confused about that, just remember usually we use 〜にあります。 When someone ask “where is 〜？” then you can answer 〜です instead of 〜にあります。 For example, when you see a picture and you want to explain where is a scissors. “はさみはつくえのうえにあります。” If someone ask you “はさみはどこにありますか or はさみはどこですか”, you can answer “つくえのうえにあります or つくえのうえです。” I hope this answer help your study.

***プールは学校にあります。 As for the swimming pool, it is in the school. The swimming pool is in the school. (哪个)游泳池在学校 like 那本书放在桌子上 ***プールは学校です。 As for the swimming pool, it is the school. (哪个)游泳池是在学校中（的） like 那本书是桌子上（的） （ * Chinese sentence are just for showing the structre. The sentences themselves are probably clumsy ones) は is a marker for emphasize, which turns to mean topic"主題“ Two sentence mean almost the same. The latter one would mean nothing or a strange thing without proper context. プールは学校にあります。sounds 有点儿奇怪 it sounds like "The swimming pool (you mentioned/are looking for) is in the school. It is different from 学校有游泳池（学校にはプールがあります）