The Floss Rule in Phonics: When to Double F, L, and S (with Word Lists + Activities)

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Do you wonder why some words are spelled with a double consonant at the end, like miss, and others aren’t (like rob)? There is actually a reason this happens, and it’s called The Floss Rule. The Floss Rule is one of the first spelling rules students learn after short vowels..

In this blog post, we’ll discuss what the floss rule is, how to teach it, and some fun activities that you can do with your students. So let’s get started!

What is the floss rule?

We often double F, L, and S after a single, short, or broad vowel at the end of a base word. Occasionally other letters are also doubled.

In kid-friendly terms:

“If a short vowel word ends in f, l, or s, we usually double it.”

Examples: off, hill, pass, buzz

When to teach the floss rule

Teach this rule right after students are confident with short vowels in closed syllables. It usually comes in Kindergarten, with continued review in Grade 1.

The floss rule gives students an easy way to read and spell many high-frequency words they’ll encounter early.

How to teach the Floss Rule

Here’s a simple way to introduce and practice this rule:

1. Anchor Chart – Start with an anchor chart that shows floss words. Go over the examples together and ask students what they notice. Then see if they can brainstorm more floss words to add.
2. Highlight the Doubled Spelling – Show students how the last letter doubles. For example, write hill and underline the ll. This makes the pattern stand out visually.
3. State the Rule Clearly – Teach students that the rule almost always applies, but there are some exceptions. Be honest about those exceptions, and explain that many come from other languages. For example, chef is a French word, so it doesn’t follow English conventions.
4. Write and Say – Have students write floss words while saying each letter out loud. This reinforces the sound-symbol connection and the doubling pattern.
5. Dictation – Use simple sentences like “I will fill the cup.” Dictation helps students apply the rule in connected text.
6. Practice Activities – Rotate through activities such as:
   • Word sorts (double vs not double)
   • Elkonin boxes (sound-to-spelling mapping)
   • Card games like Memory or Go Fish
   • Searching for floss words in decodable passages

This sequence moves from direct teaching to guided practice to independent application.

Floss Rule Words

FF words

off, cliff, sniff, puff, stuff

LL words

bell, fill, shell, tell, will

SS words

class, mess, miss, pass, toss

ZZ words (less common)

buzz, fizz

I also created a printable list of floss words that you can use for your lessons and activities. Sign up to my email list below to access the list and anchor chart.

Floss Rule Exceptions

Not every short vowel word ending in f, l, or s doubles. A few common exceptions include:

• if
• yes
• bus
• gas

There is also a rule that helps with exceptions, and that is if the final s makes a /z/ sound, don’t double it: is, as, was, has, and his.

I call these “learning words” and teach them as heart words.

Floss Rule Activities for Reinforcement

There are many activities you can find to work on the Floss Rule, mostly worksheets and games. Look out for free options on TPT too, as I always find something free when I look.

Word Sorts

This is where you want to start as sorting helps students see the patterns. You can sort non-floss words with floss words, or sort floss words by their ending.

I usually make a deck of floss words on index cards for students to use to sort and play games.

Word Hunt

Have students go on a floss word hunt. Ask them to find 10 floss words around the room or in a book/passage. You can have them highlight the words they find in a passage and write them on flashcards or a whiteboard to sort by ending.

Above I asked the student to find all the floss words in the passage and sort them into 4 boxes.

Phoneme Grapheme Mapping

This is the most effective way of working on writing floss words. In doing this activity, students see the doubled letters as one unit making one sound.

Use the word list to have students write words on a phoneme grapheme mapping template like the one pictured above. You can grab my Phoneme Grapheme Mapping Template in my shop.

Writing

Get students writing in any way you can. Whiteboards, sand trays, dictation, Elkonin boxes, and worksheets are all great ways to get them writing floss words.

I always do a quick dictation at the end of every lesson and it’s a great way to practice and assess. I have this dictation template available in my freebies library.

Games

Of course, last but not least is games! I usually just grab the deck of floss rule words I created and have students play a game using these cards. They can play a board game with them and on their turn, they need to pick up a card and read it aloud for the other players to write. You can also find lots of Floss Rule games on TPT.

Free Floss Rule Anchor Chart & Word List

? Grab my free Floss Rule word list and phonics chart by signing up below.

This chart makes it easy to send home for practice or use during small groups.

Connect It to Other Phonics Rules

The Floss Rule is just one of many spelling rules students will learn.

? See the complete guide to English phonics rules here.

Bottom Line

The Floss Rule may be simple, but it unlocks dozens of words for early readers. Teach it right after short vowels, introduce it with an anchor chart, and give students plenty of practice with writing, dictation, and games. Don’t forget to address the few exceptions. With consistent practice, students will quickly recognize and use this rule in their reading and writing.

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