Many children struggle when reading words with adjacent consonants. These are words which have two consonants side by side within a word, e.g. f l a g.
The leap from 3 sound words (e.g. h a t) to 4 sound words (e.g. l i m p) is very difficult for many beginner and struggling readers. The step to 5 sound words (p r i n t) is even greater. Being able to decode, retain and blend 4 and 5 sounds in a word is much more difficult than 3. For this reason, children need a lot of practice of this skill.
It is imperative that children can do this before they launch into learning the complex English phonic code. This means that as children learn new graphemes they can concentrate on learning the new sound/letter representation without having to struggle with the blending at the same time.