Before you read a single word of the passage, the unfinished sentence has already told you what kind of word is missing. "The roof must ______ rainwater" can only take a verb. "About ______ of the rainfall" can only take a number. "Cleaned by the roof's ______" can only take a noun phrase. The sentence eliminates half the words in the passage before you have looked at the passage — and most candidates throw that head start away by diving straight into the text and scanning every word as if any of them could be the answer.
Where this type sits officially
Sentence completion is one of the eleven question types ielts.org lists for the Reading test — the same list for Academic and General Training. It sits alongside its close relatives, "Summary/note/table/flow-chart completion" and "Diagram label completion", but it is its own named type: you are given incomplete sentences and you finish them with words taken from the passage.
One honesty note before the method: the official pages we rely on publish the list of type names and the word-limit rule, but no detailed official description of how sentence completion items are built or which skills they are said to test. Everything below about tactics is coaching — ours, labelled as such — not official wording.
What is official, and what decides marks, is the word limit:
"A word limit is given, for example, 'NO MORE THAN TWO WORDS AND/OR A NUMBER'. You will lose the mark for writing more than the word limit." — ielts.org, Academic Reading format
That second sentence is the whole penalty regime. There is no partial credit to fall back on:
"Each correct answer receives 1 mark." — ielts.org, Academic Reading format
One mark, whole or nothing. A three-word answer against a two-word limit scores the same as a blank.
The failure
Call it blind scanning. The candidate reads the incomplete sentence once, extracts a topic — "something about rainwater" — and starts hunting through the passage for anything rainwater-adjacent. They find plenty, because the passage is about rainwater. Now they are choosing between five plausible-looking words on meaning alone, under time pressure, in a section where — official statement — "no extra transfer time is given".
The grammar-first candidate does the opposite. They parse the sentence, decide the gap's word class, and only then scan — ignoring every word of the wrong class. The blind scanner searches the whole text for something the sentence itself had already narrowed to a handful of candidates.
A worked example
The passage below is written by us for this page — it is not a real IELTS text. It is shorter than a real passage; the traps are real.
Bermuda has no rivers or freshwater lakes, so for more than three centuries its households have collected rain on their roofs. Building regulations still require every new house to capture rainwater: the stepped limestone roof channels water along a series of glides into a storage tank, which in most homes sits beneath the building itself. The traditional white lime wash once helped to purify the water as it ran off, though modern roofs use synthetic paint instead. A typical roof harvests around 90 per cent of the rain that falls on it. During long dry spells, families who exhaust their tanks must buy water from private suppliers, whose trucks are a familiar sight on the island's narrow roads in late summer.
Complete each sentence with NO MORE THAN TWO WORDS AND/OR A NUMBER from the passage.
- Building regulations say that every new Bermudian house must ______ rainwater.
- A typical roof collects about ______ of the rain landing on it.
- Run-off water was once partly purified by the roof's ______.
Item 1 — the grammatically impossible tempter
The gap follows "must", so it can only take a base-form verb. Now scan. The passage's first water-collecting word is "collected" — "its households have collected rain on their roofs" — and it is perfect in meaning. It is also grammatically impossible: "every new house must collected rainwater" is not English. A blind scanner writes it anyway, because meaning was the only filter they applied. The grammar-first candidate rejected it in under a second and kept scanning to "capture" — "regulations still require every new house to capture rainwater" — which is both the right idea and the right form. Answer: capture.
Item 2 — right meaning, over the limit, mark gone
The gap sits after "about", before "of the rain" — it wants a number, probably a proportion. The passage delivers: "harvests around 90 per cent of the rain that falls on it". Here is the trap: the cautious candidate copies the whole hedge and writes "around 90 per cent" — three words and a number, against a limit of two words and/or a number. The meaning is exactly right. The official rule above still applies: "You will lose the mark for writing more than the word limit." The sentence already contains "about", so the hedge was doing nothing except costing the mark. Answer: 90 per cent.
Item 3 — fits the grammar, wrong meaning
The gap follows "the roof's", so it wants a noun phrase — something the roof possesses. Two passage nouns audition. "paint" fits the grammar perfectly: "purified by the roof's paint" reads smoothly. But the passage says the traditional white lime wash "once helped to purify the water", and that modern roofs "use synthetic paint instead" — the paint is the replacement, and the passage never credits it with purifying anything. Grammar narrows the field; it does not finish the job. The completed sentence must be true of the passage, not merely well-formed. Answer: lime wash — two words, inside the limit.
The order of operations
Grammar first, meaning second, limit last:
- Parse the sentence — decide the gap's word class before touching the passage.
- Scan for that class only — item 1 killed "collected" this way without a moment's debate.
- Verify the meaning — item 3's "paint" survives step 2 and dies here.
- Count the words — item 2's "around" survives steps 2 and 3 and dies here.
Each step catches a trap the previous one cannot.
What actually costs you
- Scanning on topic alone. The sentence told you the word class — use it, or you are choosing between tempters on vibes.
- Copying hedges and articles. "around", "the", "a" — passage padding that pushes a correct answer over the limit. The official penalty is the whole mark.
- Accepting the first grammatical fit. Well-formed is not true. Check the completed sentence against the passage.
- Changing the word's form. The safe habit is lifting words exactly as the passage prints them — rewording a completion answer is risk with no reward.
- Forgetting there is no transfer time. Official wording: "You must transfer your answers during the hour you are given for the Reading test." Every second spent scanning the wrong half of the passage comes out of the same sixty minutes.
Try one
[Try a Reading task →] — one full task, marked, no card required.