「あった」is the past tense of 「ある (be/exist/have)」
「っけ」is a particle to ask yourself or to ask somebody who shares the same memory.
「あったっけ？」 is a question to confirm the existance of something.
牛乳（ぎゅうにゅう）あったっけ？ Are there milk?
Although the verb is in the past tense, but it could be past, present or future.
Because it is a question about memory.
「明日（あした）授業（じゅぎょう）あったっけ？」 Do I(we) have a class tomorrow?
You remember that you saw the schedule yesterday, but you are not sure if there are classes tomorrow. Then ask yourself or friends.
If you ask 「明日授業ある？(Are there classes tomorrow?)」, it means you don't know.
If you ask 「明日授業あったっけ？」, it means that you knew it before but you are not sure now.