|D||Low Int. (1)||400/300||2||2||3||2||1||5||Elementary||2|
|B||High Int. (2)||480/530||4||4||-||-||3||-||Upper Level||4|
Hill, David R.; Graded (Basal) Readers -- Choosing The Best, The Language Teacher: Issue 21.05 - May 1997
Hill, David R.; Graded Readers, ELT Journal, Volume 55/3 July 2001
This table reflects several changes that have taken place since the publication of the original data in Hill (1997). Publishers have merged titles into fewer series and some new levels have been added in some series.
This table should be considered as a guide only. Hill's data reflect substantial research into the average reading difficulty of the various series' levels, whereas my modifications are simply guesses made necessary by the various publishers' changes. Teachers should always consider the needs and interests of their students.