Before selecting a preschool, ask about the potty training policy. If independent toileting is required, carefully consider if your child is developmentally ready to be potty trained. If she's not, don't force it. But if your child is able to keep her diaper dry for an hour, then she's likely ready to begin training.
http://www.parents.com/toddlers-preschoolers/starting-preschool/preparing/before-starting-preschool-what-to-know/
As your child turns age three or so you might begin wondering at what point he/she enters Kindergarten. The answer is generally that children enter kindergarten at or around age 5. This means that if your child is four and will turn five within a certain period of time then he/she will be allowed to enter kindergarten.
http://www.thelaboroflove.com/articles/at-what-age-do-children-enter-kindergarten
But, if he/she turns five after the specified date then your child will not begin kindergarten until the following year. Most states have very similar protocol, but may differ somewhat. So, as soon as your child turns four you need to begin looking into when your child is old enough to start kindergarten.
http://www.thelaboroflove.com/articles/at-what-age-do-children-enter-kindergarten
Last updated: August 2016. Most preschools will start accepting children at around age 2 ½, but that doesn't mean your child is magically ready for preschool when he reaches that age. Readiness for preschool has more to do with where your child is developmentally.
https://www.babycenter.com/0_how-to-tell-if-your-child-is-ready-for-preschool_64544.bc
Almost all kindergarten classrooms have children with birthdays that span 12 months. But because of redshirting, the oldest student in Andersen’s class is not just 12 but 15 months older than the youngest, a difference in age of 25 percent.
http://www.nytimes.com/2007/06/03/magazine/03kindergarten-t.html
Start teaching manners early, so that your child knows how to mind her p's and q's by the time she starts preschool. Greeting others, using table manners, following directions, not interrupting, and saying please, thank you, and excuse me are ways your child shows respect and consideration for others.
http://www.parents.com/toddlers-preschoolers/starting-preschool/preparing/before-starting-preschool-what-to-know/
Prior to preschool, teach your child his full name, his parents' names, and street name and number. She may even be ready to learn her phone number. Teach this by demonstrating how to dial the number on a toy phone and saying the numbers out loud. Encourage your child to do the same, providing prompts as needed.
http://www.parents.com/toddlers-preschoolers/starting-preschool/preparing/before-starting-preschool-what-to-know/
The birthday cutoffs span six months, from Indiana, where a child must turn 5 by July 1 of the year he enters kindergarten, to Connecticut, where he must turn 5 by Jan. 1 of his kindergarten year. Children can start school a year late, but in general they cannot start a year early.
http://www.nytimes.com/2007/06/03/magazine/03kindergarten-t.html
According to the apple-or-coin test, used in the Middle Ages, children should start school when they are mature enough for the delayed gratification and abstract reasoning involved in choosing money over fruit.
http://www.nytimes.com/2007/06/03/magazine/03kindergarten-t.html
Berkeley Parents Network. What Age to Start Kindergarten. Editor Note: In California, to start kindergarten at a public school and for most private schools too, children must be 5 years old by September 1. (Prior to 2011, children could start kindergarten if they were 5 years old by December 1.
https://www.berkeleyparentsnetwork.org/advice/school/fall_bday
when do kids begin kindergarten
Children enter Kindergarten at or around age 5.