The difference that decides everything: a blend keeps both sounds, a digraph makes a new one. How to teach the split, the order that works, and where students get stuck.
The one distinction students need first
A blend is two or three consonants whose sounds you can still hear separately: st in stop, bl in black, fr in frog. Say it slowly and both letters are there.
A digraph is two consonants that give up their own sounds and make one new sound together: ch, sh, th, wh, ph. There is no /c/ and no /h/ in chair — there is a third sound that neither letter makes alone.
Students who have not been given this distinction try to blend digraphs, and ship becomes /s/-/h/-/i/-/p/. It is a two-minute explanation that saves months of decoding trouble, and it is worth making explicit rather than hoping it is absorbed from examples.
Teach digraphs before blends
The intuitive order is blends first, because they seem simpler — the letters keep their sounds. In practice digraphs come first, for two reasons.
The first is frequency. sh, ch, th and wh appear in the most common words a beginning reader meets, including the, she, this and what. A student who cannot read digraphs is blocked on the first page of almost any book.
The second is interference. Once students are fluent at blending two separate sounds, they apply that habit to digraphs and produce nonsense. Teaching digraphs first establishes ‘these two letters can be one sound’ before the blending habit hardens.
A workable sequence: sh and ch, then th (both voiced and unvoiced, without naming them), then wh and ph, and only then two-letter blends, three-letter blends, and finally tch and dge.
The routine: say it, stretch it, sort it
Say it. Give the word aloud. Students repeat it. No print yet — if the letters are visible the student reads instead of listening, and you learn nothing about what they hear.
Stretch it. Say the word slowly, holding each sound. Students count the sounds on their fingers. Ship has three sounds and four letters, and noticing that gap is the whole lesson.
Sort it. Now show the print. Students decide: did those two letters keep their sounds, or make a new one? A two-column sort with blends on one side and digraphs on the other does more than a worksheet of circling, because it forces the judgement every time.
The sort is also the assessment. A student who sorts shrimp correctly — a digraph and a blend in one word — has the concept, not just the list.
Hard and soft c and g
This is the pattern most often taught as a list of exceptions, and it is not one. C and g are soft before e, i and y: cent, city, cycle, gem, giant, gym. Before any other letter they are hard: cat, cup, goat, gum.
Give students the rule and then a stack of words to test it against, including a few that break it (get, give, girl). English rules are tendencies, and a student who has met the exceptions inside the lesson is not derailed by them later.
The practical payoff is spelling, not reading: a student who knows the rule writes gentle rather than jentle.
Where students get stuck
Ending digraphs are harder than beginning ones. tch and dge follow a short vowel — watch, bridge — and students who have only met initial digraphs do not expect three letters to make one sound at the end of a word.
Blends with r and l get compressed. fr, tr, bl and cl are often heard as a single sound. Stretching helps; so does contrasting the blend word with its base (rain / train).
Voiced and unvoiced th. thin and this use different sounds and the same spelling. Do not name the difference for young students, but do include both, or this becomes an exception in their heads.