Thinking Skills Practice

OC and selective tests · For parents

What is Thinking Skills? Question types with examples

Thinking Skills is one of the three sections of the NSW OC placement test, and it is also in the selective high school test. It is less about what your child has learnt at school and more about how they think: can they follow an argument, spot a mistake, and work through a puzzle step by step?

In our practice, we sort Thinking Skills questions into three groups. Below, each group is explained with two example questions and a worked answer. Tap or click "Show the answer" after your child has tried.

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The examples on this page are written for this page only, so they do not give away the answers in our free 20-question OC Thinking Skills check. If your child has not done the check yet, it is a good place to start.

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1. Critical thinking

Critical thinking questions give a short statement or argument. Your child must decide what is definitely true, what makes an argument stronger or weaker, or where the reasoning goes wrong. The trap is choosing an answer that sounds right but is not proven.

Critical thinking: must be true

At the city zoo, the koala talk only goes ahead when a keeper is free to give it. Today, no keeper was free.
Which statement must be true?

  1. The koala talk did not go ahead today.
  2. The koala talk will go ahead tomorrow.
  3. The keepers were feeding the koalas today.
  4. No visitors came to the zoo today.
Show the answer
Answer: A. The koala talk needs a free keeper. Today no keeper was free, so the talk could not go ahead. We do not know what will happen tomorrow, what the keepers were doing, or how many visitors came.
Critical thinking: weaken an argument

The canteen manager says: "Since we started using smaller plates, less food has been thrown away. The smaller plates must be the reason."
Which statement, if true, most weakens the manager's argument?

  1. The smaller plates are easier for young children to carry.
  2. The new plates are made of strong plastic.
  3. In the same week, the school started a 'finish your lunch' challenge with a prize for the best class.
  4. Some parents think the smaller plates look nice.
Show the answer
Answer: C. If a 'finish your lunch' challenge started in the same week, the challenge could be the real reason less food was thrown away. So the smaller plates may not be the reason at all.

How to practise: when your child picks an answer, ask "How do you know that is definitely true?" If the answer needs a guess, it is probably not the one.

2. Logic

Logic questions are puzzles with a set of clues: who stands or sits where, who has what, who is telling the truth. Every clue matters, and the answer can be worked out for certain. The best tool is a quick drawing or table on the working-out paper.

Logic: ordering

Gus, Hal, Ida, Jo and Kim each have one of five lockers in a row, numbered 1 to 5.
• Gus has locker 5.
• Jo's locker is directly next to Gus's.
• Hal's locker number is 2 more than Ida's.
Who has locker 3?

  1. Hal
  2. Ida
  3. Jo
  4. Kim
Show the answer
Answer: A (Hal). Gus has locker 5, so the only locker next to his is locker 4, and that is Jo's. That leaves lockers 1, 2 and 3 for Hal, Ida and Kim. Hal's number is 2 more than Ida's, so Ida has locker 1 and Hal has locker 3. Kim has locker 2.
Logic: truth and lies

Someone left the door of the school chicken coop open. Only Pia, Theo and Uma were near the coop.
Pia says: "Theo left it open."
Theo says: "Uma left it open."
Uma says: "I did not leave it open."
Exactly one of them is lying. Who left the door open?

  1. Pia
  2. Theo
  3. Uma
  4. We cannot tell
Show the answer
Answer: B (Theo). Test each person. If Pia left it open, Pia and Theo are both lying (2 lies). If Theo left it open, only Theo is lying (1 lie). If Uma left it open, Pia and Uma are both lying (2 lies). So Theo left the door open.

How to practise: for every logic puzzle, ask your child to draw it first. Testing each option one by one, like in the chicken coop question, works for many puzzles.

3. Problem solving

Problem solving questions use numbers, time, shapes and patterns, but they need a plan more than hard maths. Your child has to work out what the rule means and count carefully.

Problem solving: number pattern

What number comes next?
3, 4, 7, 11, 18, 29, ?

  1. 36
  2. 40
  3. 47
  4. 58
Show the answer
Answer: C (47). From 7 on, each number is the two numbers before it added together: 3 + 4 = 7, 4 + 7 = 11, 7 + 11 = 18, 11 + 18 = 29, so 18 + 29 = 47.
Problem solving: careful counting

One paper cup is 10 cm tall. When paper cups are stacked inside each other, each extra cup adds 2 cm to the height.
How tall is a stack of 8 cups?

  1. 16 cm
  2. 24 cm
  3. 26 cm
  4. 80 cm
Show the answer
Answer: B (24 cm). The first cup gives 10 cm. The other 7 cups add 2 cm each: 7 × 2 = 14 cm. So the stack is 10 + 14 = 24 cm tall. (80 cm would be 8 cups standing on top of each other, not inside each other.)

How to practise: ask "What does the rule really mean?" and "How can you check your answer?" Checking is a habit that saves marks.

Why Thinking Skills is hard to teach at home

Many parents can help with spelling or times tables, but Thinking Skills feels different. The questions are in tricky English, the right answer often depends on one small word like "must" or "only", and a worked answer is easier to follow in the language you think in. That is why our free check gives worked answers in English, Vietnamese, Chinese, Korean and Thai, while the questions stay in English like the real test.

Ready to try 20 questions?

A 20-minute timer, an instant score for critical thinking, logic and problem solving, and worked answers in your language.

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Want the bigger picture? Read the OC test 2027 guide: format, dates and how to prepare.