The Times published a front-page story over the weekend about efforts in Sacramento to make kindergarten mandatory. Right now, parents in California are not required to send their children to school until they’re 6 years old. In other words, mandatory schooling starts in first grade. The bill calls for mandatory kindergarten, though the age for mandatory schooling would still be 6. This story led us to look into kindergarten a bit more. We wanted to understand how it has changed over the past few decades.