New research has linked sleep deprivation and obesity:

We sleep as much as one-quarter less than our ancestors did, with average total sleep time decreasing from 9 hours in 1900 to less than 7 hours over the past 10 years. In 2001, researchers found that sleeping less than 6 hours per night and remaining awake past midnight increased the likelihood of obesity. In 2002, a study of 1.1 million people found that increasing body mass index (BMI) occurred when habitual sleep amounts fell below 7 to 8 hours.

The relationship between sleep deprivation and increased rates of obesity in children is particularly strong.  Getting enough sleep helps focus, concentration, and learning ability.  It's also free. 

Sleep: it's not laziness, it's time well spent.