Do they have mandatory pre-first-grade education?

I was functionally illiterate at the age of five despite considerable parental investment in my education, and considering that I had achieved a twelfth grade reading level by third grade, it certainly wasn't for a lack of aptitude.

With sufficient training from an early age, I would not be surprised to hear that most five year olds can learn to write basic sentences, but I would be very surprised if most can be trained to follow written statements at the same conversational level they're capable of by that age.