Spelling is a challenging requirement of the National Curriculum for English.  Children have to be competent with a variety of prefixes (which are added to the start of words - e.g. un, dis) and suffixes (which are added to the end of words - e.g. -ly -ing -tion).  This goes alongside the requirement for them to spell tricky words correctly and make the correct choices of which phonic sounds to use in different words.  Any extra practise at home can really help to support and build on the learning that children are doing in school.