Rule 27 refers to the letters s or z. Words beginning with the sound 'z' are always spelled with z, never s.
For example: Zoo.
Watch the tutorial videos below to see how the Spelling Tools, Spelling Rule 27 and Reading Tools are used to spell challenging words.
Special Note:
Not all words will follow the spelling rule. These are called exceptions. If 90% or more words follow this rule then this is still a great tool to help become a proficient speller. Language experience will deal with the rest.