Common Mistakes in Better High School Writing: A Comprehensive Guide

The same handful of errors show up in essay after essay, year after year, across almost every high school classroom. Knowing exactly what they are — and exactly how to fix them — will do more for your grades than any amount of generic advice.

Vague or Missing Thesis Statements

A thesis like "There are many themes in this book" or "Social media has both good and bad effects" doesn't actually commit to a position. It's a topic, not an argument, and a grader has no idea what the essay is actually going to claim.

The fix: Force your thesis to take a specific, arguable stance. Instead of "Social media has both good and bad effects," try "Social media harms teenagers' attention spans more than it benefits their social connections, because constant notifications train the brain to expect instant reward." That version tells the reader exactly what you'll be proving and gives your whole essay a direction to follow.

Topic Sentences That Don't Connect to the Thesis

Related: BetterHighSchoolWriting - Essential Steps.

A common mistake is opening a paragraph with a topic sentence that describes what happens in that paragraph but never ties back to the essay's actual argument. The paragraph might be well-written in isolation, but the reader loses track of why it's there.

The fix: Every topic sentence should function like a mini-thesis for its paragraph, explicitly linked to the main claim. Instead of "The character faces many challenges in chapter three," write something like "The character's failure in chapter three proves that the author sees ambition as ultimately self-destructive" — echoing the language of your thesis so the connection is impossible to miss.

Restating Evidence Instead of Analyzing It

Dropping in a quote or a fact and then simply rephrasing it in your own words is one of the most common mistakes in student writing. It looks like analysis because there are extra sentences after the evidence, but nothing new has actually been said.

The fix: After every piece of evidence, ask "so what?" — why does this fact or quote matter for your argument? Analysis explains the significance of evidence; it doesn't just translate it. A useful habit is to make sure your sentence after a quote never just repeats the quote's content — it should say what the quote proves, implies, or reveals that isn't obvious on the surface.

Filler Phrases That Add Nothing

See also: Master Your English Writing: How to Write Better in English.

Phrases like "in today's society," "since the beginning of time," or "throughout history, people have always" are extremely common openers, and graders see them constantly. They're vague, unprovable, and delay the actual argument.

The fix: Delete the filler and start with something concrete and specific to your actual topic. Instead of "Since the beginning of time, humans have struggled with power," go straight to your real claim: "Shakespeare's Macbeth shows that unchecked ambition corrupts even a fundamentally loyal person." Specificity from sentence one signals a confident, focused writer.

Overusing Passive Voice

Sentences like "Mistakes were made" or "The theme is explored by the author through symbolism" hide who is doing the acting and often sound weaker and wordier than they need to be. Passive voice isn't always wrong, but overusing it drains energy from your writing.

The fix: Identify the actual subject doing the action and put it first. "The author explores the theme through symbolism" is shorter and more direct than the passive version. A quick test: if you can insert "by zombies" after the verb and it still makes grammatical sense (as in "the ball was thrown by zombies"), the sentence is passive — consider rewriting it in active voice unless you have a specific reason to hide the subject.

Comma Splices and Run-On Sentences

Joining two complete sentences with just a comma — "I finished the essay, I still need to proofread it" — is a comma splice, and it's one of the most common grammar mistakes graders flag. Run-on sentences, where two or more complete thoughts are jammed together with no punctuation at all, cause similar confusion.

The fix: You have several correct options: split the two ideas into separate sentences, join them with a semicolon, or add a coordinating conjunction after the comma (and, but, or, so, yet, for, nor). "I finished the essay, but I still need to proofread it" fixes the splice while keeping the connection between the two ideas.

Conclusions That Just Repeat the Introduction

Copying your introduction almost word-for-word into your conclusion is a mistake many students fall back on when they're not sure how else to end an essay. It reads as lazy and wastes the last chance to leave an impression on the reader.

The fix: Use the conclusion to explain why your argument matters beyond the essay itself — what it reveals, what questions it raises, or how it connects to a bigger idea. This is exactly the kind of pattern Better High School Writing helps students break, because a strong conclusion should feel like a natural extension of your argument, not a copy-paste of your opening paragraph.

Putting It All Together

None of these mistakes are complicated to fix once you know to look for them. The hard part is catching them in your own writing, since they're often invisible to the person who wrote them. Reading your essay aloud, checking each paragraph against your thesis, and reviewing this list before you submit anything will catch the vast majority of these issues before a teacher ever sees them.