According to an article in Newsweek,
Principals and teachers around the country are growing increasingly concerned with what they call the fourth-grade slump. The malaise, which can strike children any time between the end of the second and the middle of fifth grade, is marked by a declining interest in reading and a gradual disengagement from school. What’s causing it? Some say fourth graders get distracted by videogames, organized sports and after-school activities. Others worry that kids are burning out. No Child Left Behind has created an intense push to teach kids the fundamentals of reading. “We kill them with tests in third grade. By fourth grade, they’re tired,” says Gina Defalco, a fourth-grade teacher in Fredericksburg, Va. The slump was first noted in the 1960s, but with schools under pressure to show that kids in all grades are improving, administrators are taking a fresh look at the problem.