We did research to find the Catile levels for each grade. The data is collected from students in the United States with a size of over 500 thousand samples. Check out the results in the table below. 

The table shows the range of Catile levels suitable for a certain grade. As an example, for grade 5 students, texts with Catile levels between 795C and 1100C are suitable. And a text with a 900C complexity is good for 5th and 6th graders too.