PASSAIC, N.J. -- In a cluttered fifth grade classroom in this New York suburb, Niki Shah has spent the summer attempting an almost impossible task: teaching yoga to seven-year-olds.Each day at an annual free summer camp the city sponsors for children of mostly low-income families, Shah, a 31-year-old AmericaCorps volunteer, interrupts games of basketball and soccer to gather students in a circle around him for breathing exercises, poses such as the "the mountain" (also known as the "downward dog") and silent meditation -- difficult tasks for these first-graders with no shortage of energy or conversation.Shah, a Hindu American who was born in India and raised in Passaic, considers this his seva.