California became the first state in the nation to mandate later start times at most public schools.Gov. Gavin Newsom signed the legislation into law Sunday.The new law prohibits middle schools from starting before 8 a.m. and high schools from starting before 8:30 a.m.It's based on studies that show teens are healthier and perform better when school starts later.According to medical experts, when school starts later, children are healthier and perform better.Research shows that teenagers need eight to 10 hours of sleep per night to be healthy.Districts will have three years to shift their start times.