The DfE National Curriculum Document sets out the framework for the National Curriculum at key stages 1 and 2 and states:
Writing down ideas fluently depends on effective transcription: that is, on spelling quickly and accurately through knowing the relationship between sounds and letters (phonics) and understanding the morphology (word structure) and orthography (spelling structure) of words
The word-lists for years 3 and 4 and years 5 and 6 are statutory. The lists are a mixture of words pupils frequently use in their writing and those which they often misspell. Some of the listed words may be thought of as quite challenging, but the 100 words in each list can easily be taught within the four years of key stage 2 alongside other words that teachers consider appropriate. Spelling lists are sent home with pupils on a weekly basis as part of their homework.
The links below detail the statutory spelling work for each year group(s)