What is the best sign this skill has stuck?

Your child decodes a NEW word by its prefix: meets 'triathlon' and says three sports before anyone explains. Transfer to unseen words is the whole game.

Does uni- always mean exactly one?

It means oneness: one horn, one voice, one outfit for everyone. Sometimes the one is an idea rather than a countable object, and spotting that is a nice stretch discussion.

6th grade number prefixes (uni-, bi-, tri-)

6th grade number prefixes (uni-, bi-, tri-) worksheets

Sixth graders use number prefixes as a decoding and vocabulary tool across subjects, where bilateral, centennial, and decathlon unpack themselves on sight.

Free printable PDF worksheet, aligned to Common Core L.6.4.b.

Each print is a different sheet with its own answer key. You don't need to sign up.

The kind of words you'll complete and sort

Fill in the missing letters to make a real word, then write the whole word in its column.

brow (eyebrows grown together)athlon (swim, then bike, then run)plane (an old plane with two sets of wings)focals (glasses for reading and for distance)plet (like a twin, but one more)angle (the shape of a yield sign)lingual (speaks English and Spanish, say)te (join together)form (matching clothes for the whole team)

Columns: uni- (one) and bi- (two) and tri- (three). The clue (eyebrows grown together) picks uni for "_brow", so unibrow goes under uni- (one); the clue (glasses for reading and for distance) picks bi for "_focals", so bifocals goes under bi- (two); the clue (swim, then bike, then run) picks tri for "_athlon", so triathlon goes under tri- (three).

Every print pulls a new set of words at this level, so a make-up test or a second sibling gets a different mix.

What's on a 6th grade sheet

6th grade sheets draw from 31 words, 21 to a page. 5th and 6th grade print from the same 31 words. What changes is the standard (L.6.4.b here) and the teaching notes below.

Some of the words:

unisonuniverseunicyclebimonthlybicolorbicyclebiplanebicepstrilogytriceratops

Complete and sort. Fill in the missing letters to make a real word, then write the whole word in its column. 21 words per page.

Every version prints on US Letter or A4, with its answer key on the last page.

How to teach this

Invent nonsense words together and define them by prefix: what would a bi-snack be? A tri-homework? If your child can coin words correctly, the prefixes have become tools, not trivia.

Watch for: The prefix is a claim you can verify: count the wheels, sides, or parts and the word proves itself. Words that carry their own evidence are the easiest morphology in English. Uni- words hide the 'one' idea in different ways: one horn (unicorn), one outfit for all (uniform), one voice together (unison). The counting is sometimes an idea, not an object.

Common questions about 6th grade number prefixes (uni-, bi-, tri-)

What is the best sign this skill has stuck?: Your child decodes a NEW word by its prefix: meets 'triathlon' and says three sports before anyone explains. Transfer to unseen words is the whole game.
Does uni- always mean exactly one?: It means oneness: one horn, one voice, one outfit for everyone. Sometimes the one is an idea rather than a countable object, and spotting that is a nice stretch discussion.

Related worksheets

Ready to print one?

Need a fresh set of words? Download another copy.

Aligned to Common Core L.6.4.b. Reviewed by the One more sheet team. Content version 241, updated August 2026.

Spot a mistake on this sheet? Tell us. · About these worksheets