Daycare Ratio VS Kindergarten Ratio

In the state of Pennsylvania the ratio in a daycare for Kindergarten students is one teacher for every twelve students. However in Pennsylvania's schools, the class room sizes can go over twenty students at a time.  I wonder why is it different? These are the same kids that would be at a daycare for before/after school care.

They all have different abilities coming into the school. With this many students the teacher can not always teach to everyone if a majority is behind a select few.

I feel that we should test students before entering school then we would have a better understanding of their ability and would be able to teach them better. Then once we know where each child stands have a class separate with two teachers in order to reach each child and make sure they have the foundation for the rest of their schooling.