Vocabulary study on EnglishCentral is divided into 7 levels, from  Beginner to  Expert.
Your progress on words is tracked at the “headword” level. For example, this means you’ll study and earn progress on the headword ‘AGREE’ as you also study its other forms--‘AGREED’, ‘AGREEMENT’, and ‘AGREEABLE’.
EnglishCentral’s seven levels of difficulty map to internationally recognized levels of English study:
There are currently there over 12,000 headwords available on EnglishCentral for study, which adds up to over 80,000 words including different word forms.