This morning the children were delighted to see a number of items on my table. Many remarked excitedly that today we must be doing an experiment. I said nothing and let their curiosity get the better of them until I was asked outright ‘What experiment are we doing?’ I said we weren’t as I knew if I told them the truth we would get no work done but this little introduction made the children excited and eager to see what would be happening during the day.

30 minutes before lunch I placed the items on a table at the front of a room with bowls and spoons and baby wipes (for all the inevitable spillages).

coin clean 1



I passed around 2 coins – 1 dirty and 1 clean . (I had 3 sets so this was done quickly). Children commented on the difference between the coins.

I then asked the question;

“What do you think we will be investigating today?” The best coin cleaner

“What do you think we will use?” Ketchup, Vinegar, Water, Coke, Lemon Juice.

“What do you predict will work the best?” Children offered their ideas and why. We then did a tally on the board.


  • Explain what a fair test is
  • Why must we have a fair test?
  • How can we have a fair test? (Same amount of material – 15 spoonfuls/ Coin must be kept under for the same amount of time.)

Carry out experiment

Some options;

  • Whole class (worked well for me as it was my first time doing an experiment with the class)
  • Small groups (each group looks after 1 material)
  • Small groups (each groups has 5 bowls and does each material)

Leave the bowls for 30 – 40 minutes. (It will work quicker than this but this suited us as we went out for yard.)


Take each coin out and pass it around – let children see and comment on the results. (Leave ketchup until last)

Watch them remark at how clean the ketchup one is and discuss why ketchup is the best coin cleaner.