Use ck for the /k/ sound only right after a short vowel at the end of a word or syllable — everywhere else (after a consonant, a long vowel, or a vowel team), use k alone. Here's the rule broken down with a full, checked word list.
The rule in one sentence
If the /k/ sound comes immediately after a short vowel, spell it ck (back, kick, sock, duck). If it comes after a consonant, a long vowel, or a vowel team, spell it k alone (milk, bake, cook, week). It's the same "short vowel needs backup" logic behind the FLOSS rule for ff, ll, ss, and zz.
How to teach it: three quick checks
- Say the word slowly and listen for the vowel. Is it a short, clipped vowel sound (as in "back") or a long one (as in "bake")?
- Check what comes right before the /k/ sound. If it's a short vowel with nothing else between them, ck is very likely correct.
- If a consonant sits between the vowel and /k/, use k alone. Milk, bank, and desk all have a consonant blocking the vowel from the /k/ sound, so ck never appears there.
It also works inside longer words
The same test applies mid-word: "jacket" and "rocket" both have a short vowel right before the /k/ sound in their first syllable, which is why they take ck rather than k.
Why kids mix this up
The confusion usually isn't about the /k/ sound itself — kids know that sound early. It's that ck and k are both silent choices when a child is writing from dictation, so the only clue they have is the vowel sound right before it. A child who hasn't been taught to "listen for short vs. long" as a specific, nameable step will often guess ck for every /k/ sound, which is why words like "like" and "bike" so often get misspelled as "lick" and "bick" in early writing.
A quick practice routine
- Sort, don't just spell. Write 10-12 words on cards (mixing ck and k endings) and have your child sort them into two piles by vowel length before writing anything — this separates the listening step from the spelling step.
- Say it, stretch it, then decide. Have your child say the word, then stretch just the vowel sound ("baaaack" vs "baaake") to make the short/long contrast physically obvious before choosing a spelling.
- Build a short "consonant blocks it" list together. Milk, bank, and desk are worth a few minutes of dedicated attention, since they're the words most likely to get an incorrect ck added out of habit.
This is one of several patterns in our full English spelling rules guide. For the very similar t-vs-tch pattern, see TCH vs CH.
Free printable for this topic
Download the CK / TCH / DGE Spelling Cheat Sheet — a free PDF you can print and use today.