When do you use C vs K at the beginning of a word?

Use C before the curvy vowels A, O, and U (cat, corn, cup). Use K before the straight vowels E, I, and Y (kite, keep, sky). A helpful trick: C is curvy and goes with curvy vowels; K is straight and goes with straight vowels.

When do you use CK at the end of a word?

Use CK at the end of a word when all three conditions are met: the word is one syllable, the vowel is short, and the /k/ sound comes right after that short vowel (duck, back, stick, neck). If any condition is not met, use just K (beak has a long vowel, milk has a consonant before /k/).

What is a simple way for students to remember the C vs K spelling rule?

Teach students this rhyme: 'K takes I and E. C takes the other three.' Say it three times as a class and most students will have it memorized.

When to Use C, K, or CK in Spelling: The Simple Rule Your Students Need

by Alina A March 25, 2026

Next time a student writes "kat" instead of "cat," don't correct it right away.

Ask them: "Why did you pick k?"

They'll probably say "because k makes the /k/ sound." And they're right. It does. Their spelling is wrong, but their thinking is solid. They just don't know the rule yet.

Most of us were never taught it either. I didn't learn it until I started digging into phonics years ago, and it completely changed how I teach spelling.

The rule is so simple it almost feels like cheating.

In This Post:

The Curvy/Straight Trick for C vs. K
When to Use CK at the End of a Word
A Rhyme They'll Own by Lunchtime
Free C, K, and CK Phonics Rule Posters
The Full Phonics Rules Poster Set (266 Rules)

✏️ The Curvy/Straight Trick: When to Use C vs. K

Here's how to help your students remember whether a word starts with c or k:

The letter c is curvy. The vowels a, o, u are curvy too.

The letter k is straight. The vowels e, i, y all start with a straight line.

Curvy c → curvy vowels (a, o, u): Cat. Corn. Cup.

Straight k → straight vowels (e, i, y): Kite. Keep. Sky.

That's the whole rule for the beginning of words.

Teach it once and you'll hear your students whispering "curvy c… straight k…" while they write. Best sound in the world. 😊

Phonics rule poster showing when to use the letter C before curvy vowels a o u with picture examples

📚 When to Use CK at the End of a Word

This one comes up constantly: duck, back, stick, neck…

Have your students ask three questions:

Is it one syllable?
Is the vowel short?
Does the /k/ come right after that short vowel?

Yes to all three = ck → duck ✅ back ✅ stick ✅ neck ✅

No to any = just k → beak ❌ (long vowel) · milk ❌ (consonant before /k/)

Phonics rule poster explaining when to use CK at the end of one-syllable words with short vowels

🎵 A Rhyme They'll Own by Lunchtime

"K takes i and e. C takes the other three."

Say it three times together as a class. By the third time, they won't need you.

🤩 Free C, K, and CK Phonics Rule Posters

I made a set of C, K, and CK phonics rule posters you can print and use in your classroom tomorrow. Clear visuals, picture clues, and examples your students can reference while they write.

Not sure about the full poster set? Try these free posters first and see how your students respond.

DOWNLOAD THE FREE POSTERS →

The Full Phonics Rules Poster Set

The free posters cover the C, K, and CK rule. My Phonics Rules Poster set covers this rule and 265 others. Clear examples, picture clues, and mouth formation visuals on every poster. 266 rules total.

Teachers print the full-size version for the wall and the mini version for student notebooks. Some teachers told me their admin noticed the posters during walkthroughs because they show exactly what skill is being taught that day.

They work with UFLI and are fully aligned with the Science of Reading. K through 2nd grade.