What is an absorbed prefix?

A prefix that changes its last letter to blend with the word it joins: in- becomes im- before p or m, il- before l, ir- before r. The prefix keeps its meaning, usually not, sometimes in or into, while only the spelling absorbs.

Why does this create double letters?

The absorbed letter doubles with the base word's first letter: in+legal makes illegal, in+regular makes irregular. The seam explains spellings kids otherwise have to memorize blind.

5th grade absorbed prefixes (im-, il-, ir-)

5th grade absorbed prefixes (im-, il-, ir-) worksheets

Fifth graders sort not-words by their absorbed prefix: im- (impossible, impatient), il- (illegal, illogical), ir- (irregular, irresponsible), and learn that all three are in- shape-shifted to match the base word.

Free printable PDF worksheet, aligned to Common Core L.5.4.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.

partialresistibleluminaterationallusionproperreversiblelegiblemortal

Columns: im- and il- and ir-. Only im turns "_partial" into a real word, so impartial goes under im-; Only il turns "_luminate" into a real word, so illuminate goes under il-; Only ir turns "_reversible" into a real word, so irreversible goes under ir-.

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 5th grade sheet

5th grade sheets draw from 24 words, 21 to a page. 5th and 6th grade print from the same 24 words. What changes is the standard (L.5.4.b here) and the teaching notes below.

Some of the words:

impossibleimpatientimmobileimproperimpoliteimmortalilliterateillusionirregularirresponsible

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

Do prefix surgery: write in- + legal, then show the n absorbing into l. The double letter appears before your child's eyes, and a spelling mystery becomes a mechanical fact. Repeat with in+possible and in+regular.

Watch for: All three prefixes are the same prefix, in-, wearing camouflage. Only the spelling changes to match the next letter; the meaning rides along untouched. The absorption explains the double letters kids find mysterious: illegal has two l's because in+legal fused. Seeing the seam makes the spelling logical instead of random.

Common questions about 5th grade absorbed prefixes (im-, il-, ir-)

What is an absorbed prefix?: A prefix that changes its last letter to blend with the word it joins: in- becomes im- before p or m, il- before l, ir- before r. The prefix keeps its meaning, usually not, sometimes in or into, while only the spelling absorbs.
Why does this create double letters?: The absorbed letter doubles with the base word's first letter: in+legal makes illegal, in+regular makes irregular. The seam explains spellings kids otherwise have to memorize blind.

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Aligned to Common Core L.5.4.b. Reviewed by the One more sheet team. Content version 241, updated August 2026.

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