M.K.
From my understanding (I've asked for my own dd), the state is the one who mandates now that your child has to be 5 before sept 1st in order to start. It's a $$ issue, not a 'smarts' issue. They do not want to pay for kids to go to school until they have to.
To the previous response on Anoka-Hennepin - my bday is sept 5th and my parents took it to the board to try and get me in early and wrote letters, etc. It did not work. That was almost 30 yrs ago, before all of the budget cuts.