The
levelling process is extensive and complex, and each word has been
individually assessed by our language experts. In its simplest form, there are various factors which will affect how the level has been allocated,
either increasing the difficulty or decreasing the difficulty. We have about
15 rules that we consider when levelling a word, for example:

a) How long is the word.
b) How common is the word.
c) How close is the spelling to the pronunciation, ie how easy is it to simply
hear the spelling once the ear is familiar with English sounds.
d) Does it have, or might it have double letters.
e) Is it a homophone

… and a whole host of criteria which are applied. These criteria give us a
good indication, and the final level is always a judgement call by our
experts.