Readers 11-20 keep things simple and introduce only one new digraph (e.g. sh) per reader. This makes for sure and steady progress.
Here we introduce the first 3-letter digraph (all). As usual, to aid memory it is used many times throughout the Reader.
Some single-letter new sounds like y as in by or e as in he are also taught. This helps children read many common words.
All new sounds (e.g. ar as in Mars) and special words (like space) are learned in the context of a story. This makes them easy to remember.