The 5 Mistakes in 80% of OET Letters (and How to Fix Them)

Correct the same type of mistake in letter after letter long enough, and a pattern emerges that has nothing to do with vocabulary range or grammatical accuracy. Across the letters Dr. Mariam’s team has corrected — more than 11,000 since 2014 — the same 5 mistakes show up in roughly 80% of OET letters on first draft, and not one of them is a spelling or tense error. They’re decisions: what to open with, what to include, how much to say, what tone to use, and how to group sentences into paragraphs. A letter can be grammatically clean from top to bottom and still lose marks on all five, because none of the six official OET writing criteria score grammar alone — Language is only one of them, alongside Purpose, Content, Conciseness & Clarity, Genre & Style, and Organisation & Layout.

Watch the full breakdown: 5 Mistakes in 80 Percent of OET Letters walks through each of these five with real letter examples.

Why do the same five OET writing mistakes keep showing up?

Every OET Writing task hands you the same raw material: a set of case notes and a letter type. What varies is how a candidate converts that raw material into a finished letter, and five specific conversion decisions go wrong often enough to appear in roughly four out of every five letters this team corrects. They cluster around five of the six criteria because each one represents a different stage of turning case notes into a letter — deciding why you’re writing, deciding what to include, deciding how much to say about it, deciding what tone to use, and deciding how to group it into paragraphs. Get any one of those five decisions wrong and the mistake shows up as a specific, recognisable pattern on the page, not as a vague “needs improvement” note.

Here is the table Dr. Mariam’s team uses internally when triaging a new letter, before looking at a single grammar point:

Mistake 1: the purpose statement is missing or buried

Every OET letter type — referral, discharge, or transfer — exists to get the receiving clinician to a specific understanding or action quickly. When the opening sentence doesn’t say who the patient is and why the letter has been written, the reader has to hold the question open through the rest of the letter, picking up clues as they go. That reading tax is the opposite of what a referral letter is for.

Buried: “Mr. Alan Harris is a 68-year-old retired electrician with a history of type 2 diabetes, hypertension, and a previous myocardial infarction in 2019, who presented to the clinic today for review.” The purpose — if there is one — hasn’t appeared by the end of the sentence.

Clear: “I am writing to refer Mr. Alan Harris, a 68-year-old man, for urgent cardiology assessment following a recurrence of exertional chest pain.” The reader knows the letter type, the patient, and the ask in one sentence.

This is the mistake with the most collateral damage, because an examiner who hasn’t been told your intent in the first sentence has to infer it from everything that follows — which makes your Content selection harder for them to judge fairly as well, even if every individual fact you chose was correct.

Mistake 2: case notes get copied instead of selected

Case notes are written for the writer’s own clinical use, in dense, unfiltered shorthand. A letter is written for a different reader with a different, narrower need — and the conversion between the two requires a selection decision on every single line, not a transcription pass. The most common failure runs in both directions at once: candidates include details the receiving reader doesn’t need (a resolved childhood illness, an unrelated hobby mentioned in passing) while leaving out details they do need (a current medication that interacts with the referral reason, a specific allergy).

Run this test on every line of the case notes before you write a sentence from it: would the reader need this fact to do their job — assess the referral, continue the discharge plan, accept the transfer — or is it just present because it was present in the notes? If the answer is no, leave it out, regardless of how clinically interesting it is. Our guide to reading OET case notes covers how to pull out exactly this kind of signal from abbreviated, compressed case-note shorthand before you start selecting what goes in the letter.

Mistake 3: sentences restate information that’s already there

Conciseness & Clarity doesn’t reward short sentences for their own sake — it penalises saying the same thing twice. The most common version of this mistake isn’t an obviously bloated sentence; it’s two consecutive sentences that each carry some of the same information, so the letter reads as longer than its actual content justifies.

Padded: “The patient has been experiencing shortness of breath for the past two weeks. This breathlessness started approximately fourteen days ago and has been ongoing since then.” The second sentence adds nothing the first didn’t already state.

Concise: “The patient has reported progressive shortness of breath for the past two weeks.” One sentence, one fact, no repetition.

This mistake is easy to miss while drafting because each sentence, read in isolation, is grammatically fine — the redundancy only becomes visible when you read the two sentences together and ask what new information the second one contributes.

Mistake 4: the register drifts too casual or too formal

Genre & Style asks for a specific, narrow register: professional, warm without being familiar, and plain without being casual. Candidates miss it in two opposite directions. Some write too informally — contractions (“doesn’t,” “I’ll”), hedge-words that sound conversational rather than clinical, or a tone closer to a text message than a referral letter. Others overcorrect into dated, over-formal phrasing that reads as stiff rather than professional — stock closings and inflated vocabulary that a native clinical writer would never actually use.

Both directions cost marks under the same criterion, which surprises candidates who assume more formal is always safer. It isn’t — over-formal phrasing reads as unnatural to an examiner just as readily as contractions do. The target register sits in the middle: direct, professional, and unremarkable, the way an experienced clinician actually writes when handing a case to a colleague.

Mistake 5: paragraphs follow case-note order instead of topic

Case notes typically arrive in roughly chronological or encounter order. A letter needs a different organising principle — by topic — and the most common Organisation & Layout failure is a paragraph that groups several unrelated topics together simply because that’s the order they appeared in the source notes. A single paragraph covering medical history, current medication, and social circumstances in sequence forces the reader to track three separate threads inside one block of text.

The fix is to decide your topics first — background, current presentation, management plan, and so on — and then sort the case-note information into those topics before you start writing sentences, rather than writing sentence by sentence in the order the notes gave you the information. Transitioning cleanly from one topic-paragraph to the next is its own skill worth practising separately; our guide on transitioning between paragraphs covers the linking devices that keep topic-to-topic movement smooth once your paragraphs are correctly grouped by topic in the first place.

What this list leaves out on purpose

This is a cross-criterion roundup, not a Language-criterion catalogue — if you’re looking for the specific grammar, vocabulary, and preposition traps that recur inside individual sentences, those live in their own posts, because they’re a different kind of error with a different kind of fix. The existing OET writing common mistakes reference and the profession-specific mistakes library catalogue dozens of narrower errors by profession and letter type; this post is the five that cut across almost every letter, regardless of profession, before you even reach the sentence level.

Catching these five mistakes in your own letter

Four of the five mistakes above are things you can check for yourself with a specific, repeatable method rather than a general “proofread carefully” instruction: read only your first sentence for Purpose, line up your letter against the case notes for Content, read consecutive sentence pairs for repeated information, and name the single topic of each paragraph for Organisation. Our self-editing checklist method walks through a line-by-line version of exactly this process you can run before you submit.

Register — Mistake 4 — is the hardest of the five to catch in your own writing, because a phrase that sounds normal to you (because you wrote it) is precisely the kind of thing a second, trained reader notices immediately. The free OET Writing Checker gives you an instant first pass, but a mismatch between your intended register and how a sentence actually reads is a judgement call that benefits from a second set of eyes. Our OET writing correction service has corrected 11,000+ letters since 2014 and reviews every submission against all six official criteria — including these five patterns, which account for most of what separates a first draft from a letter ready to submit.