Well time to the hour is k/1 skill...so I am thinking the first one is k/1 but some kids aren't reading in k so not as an independent book. Then one per year after that?

I can't tell because I see my son doing the first two this year in first and the next two the following year. And then doing fractions in third. He may not go so fast but he might.

...reading is pleasure, not just something teachers make you do in school.~B. Cleary