An Angel for May by Melvin Burgess.
Tam travels back in time to his small English town at the time of World War II, where his friendship helps a traumatized girl living on a farm just outside the town.
Blossom Culp and the Sleep of Death by Richard Peck.
Blossom, high-school freshman and possessor of "second sight," helps an Egyptian princess, dead for 3500 years, to regain her tomb, and in
addition saves a suffragette school teacher from losing her job in 1914.