The floss rule: ff, ll, ss and zz

When does the rule apply?

The rule is narrow, and that is why it works. It needs three things at once: one syllable, one vowel letter saying its short sound, and f, l, s or z right after that vowel. Change any one of those and the rule switches off. "Golf" has a consonant before the f, so it gets one f. "Feel" has a vowel team, so it gets one l. "Plus" fits every condition and still has one s, which is why it sits in the exceptions table. The name is a memory hook: f, l and s are the first three letters of floss, and z tags along.

Words that follow the rule

Words that break the rule

How do you teach it?

Teach it as a spelling decision, after students read short vowel words with blends. Dictate pairs where only one word qualifies, such as "fell" and "feel", and ask students to justify each spelling before they write. The ll words outnumber the others in our list, so start there, then add ss and ff. Leave zz for last; it has the fewest words.

"Listen: miss. One syllable? Yes. One vowel, saying its short sound? Yes, /i/. Does it end in /s/ right after that vowel? Yes. Then the floss rule says we write two s's. Now try 'seal'. Two vowel letters, so the rule is off. One l."

What is the common error, and the fix?

The error runs both ways. Students write "bel" and "mes", then overcorrect with "feell" or "golff" once the rule is taught. The fix is the same check every time: count the vowel letters, then look at the letter before the final sound. One short vowel letter right before f, l, s or z means double it. Anything else means one letter.

Sort it: a hands-on activity

Write 20 words on cards, half floss words and half lookalikes (golf, feel, plus, milk, hiss, doll, wall, roll). Students sort them into "doubles" and "does not double" and say which condition failed for each card in the second pile. The all words and the long o words (roll, toll) get a pile of their own, because they double for a different reason.

How this list was built