Mini Minds Hub · Free printable
Troll Bridge Rules: Free Printable Worksheet for Year 4
- ForYear 4
- StageKey Stage 2
- CostFree
- FormatPrintable PDF
Troll Bridge Rules is a free printable computing worksheet for Year 4 (ages 8 to 9). A troll guards a bridge and follows rules. Children test those rules on each traveller, then find the bug and fix it. It needs only paper and a pencil, and page 2 gives the grown-up notes, help, a stretch idea and the answers.
It comes from the Mini Minds Hub, the free library of printables from Jaques of London, the British games and toy company that has been making games for families since 1795. Print both pages, give page 1 to your child and keep page 2 for yourself. Black and white printing works well.
What is on the sheet
Children meet a troll who follows rules at a bridge. They use cards for travellers such as a baker, a goat, a knight, a fox and a girl, some with a coin and some without. They test each card against the rules and decide who crosses. Then they answer multiple choice questions, spot the bug when a traveller sneaks across, and write a rule of their own.
- A baker with a coin
- A goat with a coin
- A knight with no coin
- A goat with no coin
- A fox with a coin
- A girl with no coin
- Using the rules, which traveller crosses?
- The goat with a coin sneaks across. Which rule fixes the bug?
A worked example with a different gate
A castle gate keeper has this rule: If a visitor carries a lantern, open the gate. Otherwise, keep it shut. A hedgehog arrives with a lantern. What does the gate keeper do?
This is a different story from the sheet, with a different rule. It shows two ways to test a rule.
Method 1: read and match- Read the rule aloud. Find the if part: the visitor carries a lantern.
- Look at the visitor. The hedgehog carries a lantern, so the if part is true.
- Do what the rule says when it is true.
- Draw two columns. Write Visitor in one and Lantern? in the other.
- Write hedgehog, then yes.
- In a third column write what the gate keeper does, following the rule.
Rules, tests and bugs
Read the rule exactly
A rule only does what it says. Children read the if part first, then check the traveller against it. They should not guess what the troll would like.
Test one card at a time
Testing means trying the rules on each case in turn and noting what happens. Going in order stops cards being missed.
Spot the bug
A bug is a mistake in the rules. If the troll does something that was not meant to happen, the rules need changing, not the traveller.
Fix it and test again
After a fix, children test the cards again. A fix can solve one problem and cause another, so they check every card, not only the one that went wrong.
What is an algorithm?
An algorithm is a set of clear steps or rules for doing a task or solving a problem. A recipe is one. So are directions to school. Computers follow algorithms exactly, so every step must be precise. The troll on this sheet acts like a very simple computer. He cannot guess what you meant. He can only follow the rules written down.
Many rules use the idea of if then. If something is true, do one thing. Otherwise, do another. Programmers call this selection. When a rule gives the wrong result, the mistake is called a bug, and fixing it is called debugging. Testing with different cases is how bugs are found. Even expert programmers do this all the time.
Skills and curriculum link
- Reading if then rules
- Testing an algorithm
- Finding bugs
- Fixing bugs
- Logical reasoning
- Writing a rule
Ideas that help with this sheet
- Rules are exactA computer does only what the rules say. If a rule is unclear or incomplete, the result may not be what the writer wanted.
- If decides what happensThe if part is a check. When it is true, one thing happens. When it is not true, the rule moves on to what comes next.
- Different cases show bugsA rule can work for one case and fail for another. Trying several different cases is how mistakes are found.
- Fixing means changing the ruleWhen the result is wrong, change the rule so it works for all cases. Then test everything again to be sure.
Key words
- RuleA clear instruction that says what should happen.
- AlgorithmA set of steps or rules for doing a task.
- ConditionThe check after the word if. It is either true or not true.
- TestTry the rules on an example to see what happens.
- BugA mistake in the rules that makes the wrong thing happen.
- DebugFind a bug and fix it.
How to use it
- Print both pages. Page 1 is for your child. Keep page 2, which has the notes and answers.
- Read the troll's rules together. Ask your child to say each rule in their own words.
- Children test each card in turn, then answer the questions and write their own rule.
- Check against page 2. Ask, "How did you know what the troll would do?" The reasoning matters as much as the answer.
- Come back another day and try writing a new rule. Repeating a familiar activity builds confidence.
Help, stretch and game ideas
If it feels too hard
Act it out. One child is the troll and holds up each card in turn. Read the rules aloud one at a time. Point to the rule, then point to the card. Ask, "Does this traveller match the rule?" Take one card at a time.
To stretch confident children
Add a new rule for a sheep with no coin. Does it still work with the goat rule? Then swap rules with a friend. Each of you makes up a new traveller to try to break the other's rules, and says how to fix it.
Make it a game
Deal the cards face down. Take turns drawing one and saying what the troll does. The other player checks the rules and agrees, or explains why not. Score a point for each correct call. Swap who plays the troll each round.
Mistakes to watch for
Watch forA child reads only part of a rule and misses the word otherwise.
Try thisRead the whole rule aloud with a finger under each word. Ask what happens if the if part is true, and what happens if it is not.
Watch forA child guesses what the troll would like instead of following the rules.
Try thisRemind them the troll only follows the written rules. Cover the picture and ask them to read the rule first, then look at the card.
Watch forA child tries to fix the bug by changing the traveller, not the rule.
Try thisSay that the traveller is fine. The rules are what need changing. Ask which rule let the wrong thing happen.
Talk about it
- What does the troll do if he follows the rules exactly?
- Why is it helpful to test every card, not only some of them?
- How did you spot the bug?
- Could your fix cause a new problem? How could you check?
- What rule would you add to make the bridge fairer?
- Where else do we follow if then rules, at home or at school?
Take it off the page
Family rules
Make an if then rule for something at home, such as bedtime or tidying up. Test it on each person in the house and see if it works for everyone.
Be the computer
One person writes three simple rules for a game. A second person follows them exactly, with no guessing. Change any rule that gives a silly result.
Draw a new bridge
Draw a different guard, such as a dragon or a giant, and write rules for who may pass. Draw three travellers and test them.
Who it is for
Parents
Sit beside your child for the first go, then let them lead. Ask them to explain what the troll does and why. If they get stuck, act it out with toys or cards on the table.
Teachers
Use it as a starter or plenary after teaching algorithms or selection. It also suits early finishers and supply cover. Page 2 gives support and stretch ideas for mixed ability groups.
Home educators
Print it as part of a wider computing plan. It pairs well with writing instructions for everyday tasks. Print again for brothers and sisters, or return to it later for revision.
Where this fits in computing
Before this sheet, children learn that an algorithm is a set of steps and that the order of the steps matters. They follow and write simple instructions, and begin to predict what will happen.
After it, children use if then ideas in programs, often with on screen tools. They combine checks, learn to repeat steps, and keep testing and debugging as they go.
Questions parents and teachers ask
- What age is Troll Bridge Rules for?
It is written for Year 4 (ages 8 to 9), in Key Stage 2. Younger children may enjoy acting it out with an adult, and older children can use the stretch idea on page 2.
- What will children practise?
They practise reading if then rules, testing an algorithm on each traveller and finding and fixing a bug. They also write a rule of their own, which builds logical reasoning.
- Do children need a computer?
No. It is a screen free computing activity that needs only paper, a pencil and scissors for the cards. It works well for quiet time, rainy days and school holidays.
- Where are the answers?
They are on page 2, which is written for the grown-up. Page 2 also has notes on how to use the sheet, help for children who find it hard and a stretch idea.
- What is a bug?
A bug is a mistake in a set of rules or a program that makes the wrong thing happen. On this sheet, children find the bug in the troll's rules and choose a fix.
- Can teachers use it in class?
Yes. It works as a starter, plenary, early finisher task, homework or table activity. It needs no preparation beyond printing and cutting out the cards.
- Is it free to print?
Yes. It is free to print for home and classroom use, and black and white on plain A4 paper works well. You can print it again for brothers, sisters or revision.
Preview the full PDF
Made by Jaques of London, making games for families since 1795. A printable supports classroom learning and does not replace a teacher.