PSLE Science: Answering 'Explain' Questions with the Keyword Method

A parent showed me her daughter's marked paper last term, genuinely baffled. The girl is bright — top of her class in the topical tests — and yet the same comment kept appearing in the margin of Booklet B: "explain, not describe". Two marks here, one there. By the end of the paper it added up. "She knows all of it," the mother said. "Why does she keep losing marks?"

She wasn't losing them on knowledge. She was losing them on the word explain, and on not landing the one keyword the marker was paid to look for. That's the most fixable problem in the whole Science paper, and it's the heart of what people call the keyword method.

Why "explain" is the word that decides the mark

PSLE Science open-ended questions all carry a command word — the verb that tells your child exactly what kind of answer to write. State. Describe. Explain. Suggest. Compare. Children skim past it and start writing whatever they know about the topic. That's the first leak.

Three of these come up constantly, and the difference between them is real:

• State (or name, give): just hand over the fact. No reasoning. "Name the gas plants take in for photosynthesis." → Carbon dioxide. Done. A child who writes a whole paragraph here is wasting time they'll need later.
• Describe: say what happens, often in order — but don't say why. "Describe what happens to the temperature of the water in the first five minutes." → The temperature rises, then stays the same. You report; you don't reason.
• Explain: give the why — a cause and its effect, linked. This is where the marks live, and where children most often write a describe answer by mistake. "Explain why the temperature stays the same even though the water is still being heated" needs a reason, not a restatement.

Mix these up and you lose marks even when the science in your head is perfect. A child who describes when asked to explain has answered a different question. The marker can't give credit for a good answer to the wrong instruction.

The three jobs every "explain" answer has to do

Strip away the frameworks the tuition centres sell under different names, and an explain answer is doing three things. Miss one and the mark slips.

One: name the concept. Every question is secretly about a single idea — evaporation, conduction, a complete circuit, an opaque object blocking light. "The water disappeared" names nothing. "The water evaporated" puts the concept on the table.

Two: build the cause-effect chain. Explain means because. Heat is gained or lost; it doesn't just "move". Particles gain energy, move faster, and spread further apart. The chain has to run from cause to effect, in order, so the marker can follow the logic.

Three: land the exact keyword. This is what people mean by the keyword method. The mark scheme has a specific word printed on it, and a beautiful sentence that dodges that word still scores zero. "Gets bigger" doesn't score when the scheme says expands. "Goes hot" doesn't score when the scheme wants gains heat. The keyword isn't a nice-to-have — for most explain questions, that precise word is the mark.

Before and after, across four topics

Theory is cheap. Here are the same near-miss answers I see leak marks every year, next to the version that scores. Watch the keyword doing the work each time.

Heat transfer. A metal teaspoon is placed in a cup of hot tea. Explain why the handle of the spoon becomes warm. (2 marks)

Loses the mark: "The heat travels up the spoon to the handle."

Scores: "Metal is a good conductor of heat. Heat is conducted from the hot tea, along the spoon, to the handle, so the handle gains heat and becomes warm."

"Travels up" is the child's everyday language. Conductor, conducted, gains heat is the science the marker is told to find. Same understanding, different words on the line.

Evaporation. Wet clothes hung outside on a sunny, windy day dry faster than on a cool, still day. Explain why. (2 marks)

Loses the mark: "Because it is sunny and windy."

Scores: "On a sunny day, the clothes gain heat faster, so water evaporates faster. The wind also carries the water vapour away from the clothes, allowing more water to evaporate, so the clothes dry faster."

The weak answer points at the conditions but never names evaporation or links cause to effect. The strong one names the concept and chains it: heat → faster evaporation → vapour carried away → dries faster.

Light and shadows. A child stands in front of a torch and a shadow forms on the wall behind her. Explain why a shadow is formed. (2 marks)

Loses the mark: "Because she is blocking the light."

Scores: "The child is an opaque object that blocks the path of light. Light travels in a straight line and cannot pass through her, so a dark area — a shadow — forms on the wall behind her."

The keywords are opaque, blocks the path of light, and travels in a straight line. "Blocking the light" gestures at the idea; it doesn't name the property of the object or the behaviour of light.

Electrical systems. In a circuit, the bulb does not light up. The wires and battery are working. Explain why the bulb does not light. (1 mark, given there is a gap at the switch)

Loses the mark: "Because the electricity cannot go through."

Scores: "The circuit is open (incomplete) at the switch, so electric current cannot flow through the circuit and the bulb does not light up."

Open circuit, incomplete, current cannot flow — those are the words on the scheme. "Cannot go through" is the same thought without the science.

See the pattern in all four? The child usually knows the answer. The mark turns on whether they translated that knowing into the marker's exact language.

Reading the marks in the bracket

The number in the bracket is an instruction, not decoration. A 2-mark explain question almost always wants two distinct points — usually a cause and its effect, or two separate links in the chain. If your child has written one short sentence for a 2-mark question, something is missing. Go back and find the second idea before moving on.

The reverse trap is just as costly: writing a full paragraph for a 1-mark state question while the heavy 3-mark explain question further down gets one rushed line. Time bleeds on the cheap marks and the expensive ones go unanswered. The bracket tells you where to spend the energy.

This is the same instinct careful problem-solvers use in maths — read what the question is actually asking before reaching for a method. If you want the bigger picture of how these open-ended marks add up across the paper, I've written a fuller guide to PSLE Science open-ended questions, and a separate one on how the PSLE AL scoring system works so you can see why a couple of these dropped marks can nudge a child from one band to the next.

Common mistakes that quietly cost marks

Describing when asked to explain. "The temperature increased" answers a describe; an explain needs what caused it to increase. This is the single most frequent margin note I write.

Restating the question as the answer. "The ice melted because it melted" hands the question straight back. The marker needs the cause — the ice gained heat from the surroundings and melted.

Missing the one keyword the answer hangs on. "The ice got smaller" instead of "the ice melted as it gained heat". "The plant grew towards the light" instead of "the plant grew towards the light because it needs light for photosynthesis". A graceful sentence that avoids the keyword still scores nothing.

Confusing the look-alikes. Evaporation versus boiling. Melting versus dissolving. A conductor versus an insulator. An open circuit versus a short circuit. These pairs feel interchangeable in everyday life and are ruthlessly separate on the mark scheme.

Writing a model answer into the wrong scenario. A child memorises the metal-spoon conduction answer, then a question asks about a plastic ruler, and they call it a good conductor anyway — when the science needs a poor one. The concept has to be re-read into the actual situation every single time.

What to do this week

Pull out your child's last marked Science paper and turn to Booklet B. Ignore the score in the corner. For each dropped mark on an explain question, ask one thing together: did the answer name the concept, build the cause-effect chain, and land the keyword — or did it skip one? Nine times out of ten you'll find the science was in their head and never made it onto the line.

Then take three of those questions and have your child re-answer them — out loud first, then written. Hearing "because it is hot" become "the spoon gains heat by conduction, so the handle becomes warm" is the moment the keyword method clicks. Keep a running list of the exact keywords for each topic they keep missing, and quiz those for five minutes a few times a week. Done steadily, the explain questions stop being where marks leak and become where they're banked.