For those of you who have questions about prioritizing vocabulary learning, I'm linking the General Service List and the Academic Word List.
The General Service List covers the 2000 most common words in English (often called "sight word" if you teach to young learners).
The Academic Word List I'm putting up breaks the most common words used in academic writing into 9 levels of frequency, so learners can prioritize their vocabulary learning.
Unfortunately I've had them so long that I don't have source references for them. :-(
Happy reading!