The Wish Master by Betty Ren Wright

Sometimes you have to be careful what you wish for . . . "An adventure story with a hint of the supernatural . . . full of action and suspense" (School Library Journal).
Most years Corby likes summer vacation, but not now. He's stuck at his grandparents' house in Wisconsin, where his grandfather constantly reminds him how timid he is and how different his father was at his age. And his new friend Buck seems to think he's chicken, too, just because he'd rather be sensible than risk getting hurt. To prove he's tough, Corby joins Buck for a nighttime journey into the woods to find the Wish Master, a fierce, giant statue that is rumored to grant wishes.

Soon it seems as if the Wish Master does have special powers-though it doesn't always get things exactly right. When Corby wishes for a puppy, a mangy stray comes into his life. He soon grows attached to the loyal mutt. Then the dog gets Corby in big trouble, and Corby decides it's time to wish for what he really wants: to go home. But will this wish bring more harm than good?