The following charts show how often different types of library books are checked out, on average, per book, for each school level. The averages were caluclated using the last 3 years of circulation history, encompassing more than 3.2 million checkouts.
English Books : 
Easy
Level  1 Year Yotal  Year to Date 
ECE  1.3444 times  1.1598 times 
Elementary  1.0829 times  0.9342 times 
K8  1.2045 times  1.0391 times 
Middle  1.1338 times  0.9781 times 
612  0.3391 times  0.2926 times 
High  3.5244 times  3.0404 times 

Easy Fiction
Level  1 Year Yotal  Year to Date 
ECE  0.9542 times  0.8232 times 
Elementary  0.9604 times  0.8286 times 
K8  1.4716 times  1.2695 times 
Middle  1.4183 times  1.2235 times 
612  0.3529 times  0.3045 times 
High  1.4248 times  1.2291 times 

Easy NonFiction
Level  1 Year Yotal  Year to Date 
ECE  0.2619 times  0.2259 times 
Elementary  0.8689 times  0.7496 times 
K8  1.0706 times  0.9236 times 
Middle  0.6316 times  0.5448 times 
612  0.1389 times  0.1198 times 
High  0.2730 times  0.2355 times 

Biography
Level  1 Year Yotal  Year to Date 
ECE  0.5238 times  0.4519 times 
Elementary  0.3950 times  0.3408 times 
K8  0.2470 times  0.2131 times 
Middle  0.2927 times  0.2525 times 
612  0.1190 times  0.1027 times 
High  0.0888 times  0.0766 times 

Fiction
Level  1 Year Yotal  Year to Date 
ECE  1.2681 times  1.0940 times 
Elementary  1.1571 times  0.9982 times 
K8  0.9977 times  0.8607 times 
Middle  0.8361 times  0.7213 times 
612  0.3299 times  0.2846 times 
High  0.3290 times  0.2838 times 

NonFiction
Level  1 Year Yotal  Year to Date 
ECE  0.9867 times  0.8512 times 
Elementary  0.9052 times  0.7809 times 
K8  0.6586 times  0.5681 times 
Middle  0.4060 times  0.3502 times 
612  0.1538 times  0.1327 times 
High  0.1437 times  0.1239 times 

Reference
Level  1 Year Yotal  Year to Date 
ECE  2.3611 times  2.0369 times 
Elementary  0.3779 times  0.3260 times 
K8  0.0903 times  0.0779 times 
Middle  0.1502 times  0.1295 times 
612  0.0281 times  0.0242 times 
High  0.0610 times  0.0526 times 

Story Collection
Level  1 Year Yotal  Year to Date 
ECE  0.9333 times  0.8052 times 
Elementary  1.1369 times  0.9807 times 
K8  0.6671 times  0.5755 times 
Middle  0.4333 times  0.3738 times 
612  0.2053 times  0.1771 times 
High  0.1307 times  0.1127 times 

Spanish Books : 
SPA Easy
Level  1 Year Yotal  Year to Date 
ECE  0.3694 times  0.3186 times 
Elementary  1.2739 times  1.0990 times 
K8  1.9774 times  1.7059 times 
Middle  0.4526 times  0.3904 times 
612  0.3035 times  0.2618 times 
High  5.0528 times  4.3590 times 

SPA Easy Fiction
Level  1 Year Yotal  Year to Date 
ECE  0.3333 times  0.2876 times 
Elementary  1.0375 times  0.8951 times 
K8  2.3692 times  2.0438 times 
Middle  0.0417 times  0.0359 times 
612  0.3333 times  0.2876 times 
High  6.3846 times  5.5079 times 

SPA Easy NonFiction
Level  1 Year Yotal  Year to Date 
ECE  0.0000 times  0.0000 times 
Elementary  0.7410 times  0.6393 times 
K8  1.1529 times  0.9946 times 
Middle  0.0000 times  0.0000 times 
612  0.5333 times  0.4601 times 
High  1.3333 times  1.1502 times 

SPA Biography
Level  1 Year Yotal  Year to Date 
Elementary  0.2389 times  0.2061 times 
K8  0.4371 times  0.3770 times 
Middle  0.4485 times  0.3869 times 
612  0.2431 times  0.2097 times 
High  0.1121 times  0.0967 times 

SPA Fiction
Level  1 Year Yotal  Year to Date 
ECE  0.5556 times  0.4793 times 
Elementary  0.8308 times  0.7167 times 
K8  0.7399 times  0.6383 times 
Middle  0.9207 times  0.7943 times 
612  0.3085 times  0.2661 times 
High  0.3593 times  0.3100 times 

SPA NonFiction
Level  1 Year Yotal  Year to Date 
ECE  0.1402 times  0.1209 times 
Elementary  0.6041 times  0.5212 times 
K8  0.6472 times  0.5583 times 
Middle  0.7374 times  0.6362 times 
612  0.1747 times  0.1507 times 
High  0.5970 times  0.5151 times 

SPA Reference
Level  1 Year Yotal  Year to Date 
Elementary  0.0987 times  0.0852 times 
K8  0.0248 times  0.0214 times 
Middle  0.0349 times  0.0301 times 
612  0.0169 times  0.0146 times 
High  0.0714 times  0.0616 times 

What are they?
Expected Checkout Rates are estimates of how many books an average librarian would check out at a particular school based on the types and numbers of books in that collection.
Why do we use them?
We have found that schools with more books per student also check out more books per student, on average. Therefore, comparisons of checkout rates between two schools can be biased if one school has a larger collection than the other. Instead we prefer to compare a school's checkout rate to how we would expect an "average" librarian to perform with that particular collection.
How are they calculated?
We took three years of checkout information and determined that average number of times each type of book was checked out at each school level (e.g. Elementary schools, Middle schools, etc.) These average circulation rates, which can be seen in the section above, are then multiplied by the number of books for each type at the school, and divided by the number of students there.
For example, Fiction books at Elementary schools are checked out 1.19 times per year, on average. So if Elementary School "X" has 500 Fiction books and 200 students, we would expect the average librarian at this school to check out 2.975 Fiction books per student. ( (500 X 1.19) / (200) )
We then add of the expected rates for each type of book to determine the overall expected rate for that school, and then apply an aging factor to account for the disparate rates of circulation for newer versus older books. This final "expected checkout rate" is then compared to a school's actual rate to provide a neutral, biasfree basis of evaluation.