Having 2 kids in primary now there is more to it than counting to 10, knowing alphabet. I know no one here is saying that, but I find most people see the requirements in a one dimensional, myopic way.
What I find equally, if not more important is behavioural, neurological and social aspects.
Can they sit on the floor for half an hour without fidgeting, calling out?
Do they have good impulse control?
Can they continue to hold their attention to a task without supervision?
Can they continue to hold their attention to a task while it's noisy/hot/crowded?
Can they follow tasks with 2/3/4/5 sets of stages or instructions?
Do they share in their play?
Can they actively pull back from play fighting? (let me tell you mothers of boys - you are going to encounter this).
Do they feel comfortable approaching teachers if they have wet themselves/are being picked on/don't have any lunch?
Can they verbalise their feelings on a basic level?
Can they verbalise why they did something on a basic level?
Do they understand the bare basics of personal safety and space? What is a good and bad touch, what should they do?
Those are just a few that come to mind....