David Brin's Out Of Time

It's 2336, and the future needs heroes! They must reach back in time to find them. What if they come for you? In 2336 there is no war, no pollution, no disease, no crime-but utopia has a price...

As part of a desperate battle to save an imperiled twenty-fourth-century Earth, four teenagers from the planet's past join forces on a mission to the edge of the solar system to a small scientific base overrun with cute but dangerous alien pests.

In the year 2345, young heroes yanked from the twentieth century and beyond must fight an enemy more skilled, cunning, and dangerous than they ever imagined. But these young heroes are the world's only hope. Adam O'Connor is no stranger to trouble. His most recent stunt-setting off firecrackers in a teacher's car-has landed him a school suspension. But even Adam can't have predicted the brand of trouble that awaits him when he's yanked to 2345 to attend an historic meeting between humans and the warlike K'lugu and Devlins. Will he display the "grit" that only a select few in his generation possess? Will he become the hero that he is destined to be?