I'm trying to remember the name of the book or series involving time travel through dreams. It would have been published pre-2004-2010 and was a young-adult book. I can't recall it having won any awards at the time of reading.
The plot involves a boy either in middle or high school who is part of a secret society who protect/travel through time to maintain it without messing it up or stop people from changing it. The story starts with him being told that although he has accomplished enough to earn some very high rank and "wings" he needs to to one more thing before he receives them. He needs to train some girl to be an new member. I seem to recall her at some point being in the same class and some scene with a pen (I think). They time travel by sleeping and their minds are transported and they either take the appearances of others or inhabit their bodies for a time. At some point the two travel to England and they almost get caught so they go into a room and pretend to be making out to have an excuse for why they are in the room. I recall that during this scene the boy's father wakes him up causing him to leave his partner as he was worried he wasn't waking up.
Things happen and it turns out the father used to be a part of this secret society until something went wrong with his partner, who is now the villain. I think there was something about going back in time during a plague and either the dad or his partner gives a vaccine for it to a women. I can't exactly recall what happens just mention that being the only survivor would drive her crazy or make her seem a witch to others. I don't remember where in the book, but the boy tells the girl that they must be careful in their interactions in the past so they don't mess with it and gives an example of some inventor and his invention never being invented due to time meddling.
Things happen and in the end the boys father decides to join his son to fight the big bad they succeed (either completely or to a degree) and the boy gets his wings. Actual wings as I recall.
I can't recall if this was a standalone book or the first in a series. I hope someone can help me remember the name of the book.