The key idea behind fluency is that it follows instruction. So whenever you see a fluency expectation in the Common Core, recognize that it sits within a greater body of concept development.
Sometimes the concept is developed within a grade level and the fluency is a small part of the greater work and sometimes the fluency grows out of concepts and skills that are developed over several grades .
In Kindergarten students are expected to fluently add and subtract within 5. But if you look at K.OA.2-4, you see that Kindergarteners are doing a lot of work decomposing 10's, creating partners to 10, and exploring addition and subtraction within 10 using objects and drawings.
In 4th grade, students should be able to fluently add and subtract multi-digit numbers within 1,000,000 using the standard algorithm. This fluency expectation is an extension of the concepts and fluencies developed in grades K through 3.
The following document outlines the fluency expectations for Kindergarten through Algebra II. The concept of fluency can be applied to any concept that we have developed. This chart outlines some essential fluencies for each grade. However, fluency can be applied more broadly to help students build automaticity with any concept that they are learning in math.