The Whistling Wind by Susan & Wendy Mitchell

Callum loves living on a farm, but more than anything in the world, he wishes he could whistle. His father takes their sheepdog, Jet, out into the fields to help round up the sheep and he whistles all the time, commanding Jet to run this way and that. Callum practices lots, but just cannot do it. Until one stormy night, when he wakes up to the sound of the wind blowing through the house, teaching him in the most unexpected of ways. The funny thing is this special, natural sort of magic just seems to vanish – poof!- the moment a grown-up is around…