Readers 1X-10X are 10 new stories, set at the beginner level (as 1-10). These were requested by teachers to provide children with more practice on simple sounding words before moving on to the next level (11-20) with its many digraphs.
Without introducing any new spelling principles, the Readers 1X-10X provide more long words which can be simply sounded out.
There are hardly any new special words in the 1X-10X series. The basic principles of sounding out are consolidated with more sounding words and longer sounding words.