Teaching the FLOSS Rule So It Actually Makes Sense (Double f, l, s Explained)

One of the best parts of using Orton-Gillingham, Science of Reading, or LETRS is that all three approaches rely on rules to teach both reading and spelling.

When it comes to short vowel rules, there are four you will typically teach:

• the FLOSS Rule
• the CH Rule
• the J Rule
• the K Rule

Here, we are focusing on the FLOSS Rule and how to teach it.

FLOSS Rule Defined

The FLOSS Rule says: Double the f, l, and s at the end of a one-syllable word following a short vowel.

Teaching the FLOSS Rule

Start with Words That Clearly Follow the Rule

At the beginning, it’s important to stay with words that clearly match the pattern. And, I like to use just one vowel sound at a time as well. Once the student notices the pattern, show it with more vowel sounds as a progression.

Words like:

• grass, class, mass, pass, sass, then boss, floss, moss
• bell, pell, sell, dell, then pill (remember, a will change the ll sound, as in ball, and so will u, as in bull (see below)
• fluff, cuff, puff, duff, then cliff (you can also use nonsense words to illustrate the rule and make sure the student understands the rule, not just memorizes words).

The letter z also follows this rule. There are so few words that have z, it can be included, but it’s not always included in the written/spoken rule.

• buzz, fuzz

Using these words in this way makes the rule visible and consistent. Students can hear the short vowel, see the double letter, and begin to connect the two.

You can find FLOSS Rule practice in Scope and Sequence Workbook 1. Build a strong foundation covering consonants, short vowels, and essential early rules like C&G, Closed Syllables, and FLOSS. 

Understanding Exceptions

As with any rule in English, there are exceptions.

There are one-syllable words that do not double, even though it seems like they should:
if, clef, pal, nil, gas, this, us, thus, yes, bus, pus, plus

There are also words that double, but do not follow the FLOSS pattern:
ebb, odd, egg, err, shirr, buzz, fuzz, fizz, jazz

The z words can be handled in different ways. Some teachers choose to include them as part of the rule, while others teach them as exceptions. Either approach works, as long as it is consistent.

The key is not to begin with these exceptions. First, students need a clear understanding of the rule itself.

What About Multi-Syllable Words?

Words like address often raise questions.

This is not the FLOSS Rule. FLOSS applies only to: one-syllable words with a short vowel

The double s in multi-syllable words comes from other spelling patterns, not this rule.

Suffix Connections

You will also see double s when working with suffixes like: -less and -ness

This is a great opportunity to begin connecting this rule to later morphology work, where students start to see how endings function across larger word structures.

Where To Be Careful

There are several situations where words may look like they follow the rule but behave differently. These are important, but not where you begin.

For example, words with a before l: fall, ball, squall

Here, the vowel does not sound short in the same way, which can confuse students early on.

You will also see this with u in words like: full, pull

The vowel can take on an /oo/ sound, which is still considered a short vowel sound, but it’s not where you want to start when introducing the rule.

The same is true for words like: knoll, scroll

The vowel sound shifts, and these do not follow the short vowel pattern in a way that supports early instruction. These are Wild Old words.

These words absolutely have a place, but they come later, once the core pattern is solid.

What if my student finds an exception I didn’t teach?

I see a lot of questions that ask, “What do I tell a student who asks, why is this word not following the rule?”

The answer is there are always exceptions (there is no exception to there being exceptions to every rule!). This is not what you tell a student right away. First, establish the rule, then get into exceptions.

The goal is to ease into the information and add more information after the rule is digested.

Repetition is key to getting this information to be automatic – making sure that students not only know the rule by definition but can write words by following the rule (writing the words by hearing them through dictation) and reading the words (sight).

A Final Word: Practice Is What Makes This Automatic

Repetition is what makes the FLOSS Rule usable.

Students need to:

• read the words
• write the words
• hear the sounds
• apply the pattern

It’s not enough to just know the rule. They need to be able to use it automatically in both reading and spelling.