Fixing Sentence Fragments and Run-Ons
A 45-minute grammar lesson on where a sentence starts and stops. Students learn the subject-plus-predicate-plus-complete-thought test, spot fragments and run-ons, and repair both in real writing rather than only labeling them.
Grammar
Subject
Grades 3-5
Grade Level
45 minutes
Duration
Sentence Structure
Topic
On this page: Materials · Warm-Up · Direct Instruction · Guided Practice · Independent Practice · Assessment · Closure · Related Resources
Learning Objectives
By the end of this lesson, students will be able to:
- Test a group of words for a subject, a predicate, and a complete thought
- Identify a sentence fragment and explain which part is missing
- Identify a run-on sentence and explain where it should be divided
- Repair fragments and run-ons in three or more different ways
Materials
- Sentence Fragments Worksheet — one copy per student
- Run-On Sentences Worksheet — one copy per student
- A paragraph of student writing, real or teacher-written, with both errors in it
- Index cards or scrap paper for the exit ticket
Vocabulary
- Sentence — a group of words with a subject and a predicate that expresses a complete thought
- Subject — who or what the sentence is about
- Predicate — what the subject does or is
- Fragment — a piece of a sentence punctuated as if it were a whole one
- Run-on — two or more sentences joined with no punctuation or with only a comma
- Conjunction — a joining word such as and, but, so, or because
Preparation
Write a mixed set of eight items on the board before class — some complete sentences, some fragments, some run-ons, unlabeled and out of order. Sorting a mixed set is the actual skill; a page of fragments alone teaches students that the answer is always fragment.
Prepare one short paragraph with both errors woven into otherwise correct writing. If you use real student work, retype it so it is anonymous. Repairing a paragraph is the difference between recognizing an error on a worksheet and catching one in a draft.
Write the three-part test where it will stay visible:
- Is there a subject — who or what?
- Is there a predicate — what they do or are?
- Does it make sense on its own, with nothing before or after it?
Warm-Up
5 minutes. Put two items on the board and read them aloud in a flat voice, exactly as written: “Ran across the yard.” and “The dog ran across the yard he was chasing a squirrel he did not catch it.”
Ask what is wrong with each. Students hear both problems immediately — the first leaves you waiting for who, the second never lets you breathe. Their ears are already correct; the lesson is about giving that reaction a name and a test.
Name them: the first is a fragment, the second is a run-on. Both are boundary mistakes, which is why they are taught together.
Direct Instruction
12 minutes. Teach the three-part test, then apply it aloud to the eight board items. For each one, say the test out loud rather than announcing a verdict:
- “Ran across the yard.” — predicate yes, subject no. Who ran? Fragment.
- “Because I forgot my lunch.” — subject yes, predicate yes, complete thought no. It leaves you waiting for the rest. Fragment.
- “The bell rang we lined up.” — two complete thoughts, no punctuation between them. Run-on.
The second example is the one worth the most time. Students expect a fragment to be short and are genuinely surprised that a long group of words with a subject and a verb can still be one, and subordinate-clause fragments are by far the most common in real writing.
Then teach repair, and teach that there is more than one right answer. A fragment can be fixed by adding what is missing or by attaching it to the sentence beside it. A run-on can be fixed with a period, with a comma plus a joining word, or by rewriting. Show at least two repairs for the same run-on and ask which sounds better — correctness and choice are different questions, and students should meet both.
Guided Practice
13 minutes. Students work in pairs through the first section of the Sentence Fragments Worksheet, then the Run-On Sentences Worksheet, while you circulate.
Require the diagnosis, not just the label:
- Fragment or run-on?
- Which part is missing, or where exactly does one sentence end and the next begin?
- Write the repair.
Have partners read each item aloud to each other before deciding. Reading in a flat voice, with nothing added, is the test in practice — students who read a fragment with the previous sentence attached will hear a complete thought that is not there.
Stop the class on any item where several pairs disagreed, especially a because-clause. Those are worth resolving publicly.
Independent Practice
10 minutes. Students finish the worksheets alone, then take the prepared paragraph, mark every fragment and run-on in it, and rewrite it correctly.
The paragraph is the point of the lesson. On a worksheet the errors are isolated and already suspicious; in a paragraph they sit among correct sentences and have to be found. That is the version of the skill students need on their own drafts, and it is markedly harder than the exercises that precede it.
Assessment
5 minutes. Exit ticket with three items: one fragment, one run-on, one correct sentence, unlabeled. Students name each one and repair the two that need it.
Including a correct sentence is deliberate. A student who marks it wrong has learned that the task is to find an error rather than to apply a test, and would have scored full marks on a page where every item was broken.
Closure
3 minutes. Return to the two warm-up items and have the class repair each one two different ways. Close on the standing routine: when you finish a draft, read it aloud one sentence at a time, and stop where you would naturally breathe.
Differentiation and Accommodations
- Extra support: split the lesson. Teach fragments today using only missing-subject and missing-predicate examples, and save subordinate-clause fragments and run-ons for a second day. Colored highlighting — subject in one color, predicate in another — makes a missing part visible rather than abstract.
- Extension: ask students to repair the same run-on three ways (period, comma plus conjunction, rewrite) and argue for the best version. That moves the work from correctness into style, which is where sentence variety comes from.
- Common difficulty: the comma splice. Students who learn that a run-on needs punctuation often add a comma and stop. Be explicit that a comma alone cannot join two complete sentences — it needs a joining word with it, or it needs to be a period.
- Watch for: students who cannot find the subject at all. That is an earlier skill and needs its own work first; the subject and predicate worksheet is the prerequisite, not extra practice.
Extension Activities
Make the read-aloud check part of your editing routine rather than a one-day lesson. Fragments and run-ons are caught in revision, not prevented in drafting, and the students who improve are the ones who reread out loud out of habit.
Once boundaries are secure, compound sentences are the natural next step: the same joining words that repair a run-on are what let a writer combine short choppy sentences on purpose.
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