Set 1 teaches short vowels, long vowels, initial blends, with optional manipulative activities in each book (if you have some sort of letter blocks). Our family likes all of these cute stories!
Groups of phonetically-similar words are practiced in short sentences to make an interesting story.
About Phonics Readers (see also this blog post about types of readers):
In comparison, some typical phonics readers have just strings of sentences that do not relate to the rest of the pages in the book (in other words no plot line). But we sell the kind of phonics readers that DO have a storyline while using the phonetically-similar words.
Recommended for Grade 1. Set of 16 readers plus 1 teacher’s guide.
Note: Letter blocks are NOT included but you can find them easily elsewhere if you want the hands-on component to these readers. (Our family just tends to use the readers as readers without manipulatives.)