British Council-Word Family

The EU has done a lot of research into languages .Here is a WORD FAMILY FRAMEWORK based on CEFR. I believe that is quite useful for English language teacher. It shows the relationship between the level of proficiency and the frequency of usage of particular words.
First I entered "able" :

 

Then I entered "document":

 Here are the results. You can access the website by clicking the following link:

http://www.learnenglish.org.uk/wff/