Lesson 6: Spy School – Invisible Ink, Cyphers and Codes

May 22, 2020 by Minerva Tutors,

Welcome to Spy School


Here at Spy School, our resident Secret Agent trainer, Sadie, taught us about four types of secret code used throughout history – from the time of the Tudors to the present day. With your help, she cracked the clues and stopped a gross SLIME EXPLOSION attack in London! Here’s a reminder of the different codes and how you can write your own secret notes…

You can also watch the Spy School video on Minerva Tutors TV


Who knew it was so easy to write your own invisible notes at home?! All you need to write your note is a piece of blank paper, a lemon and a cotton bud; and to read it, a heat source like a lamp or (if you have an adult to help you) a clothes iron.

  • Squeeze lemon juice into a small cup or bowl
  • Dip your cotton bud into the lemon juice
  • Use the cotton bud to write your note (dip it into the juice every now and then)
  • Let it dry!
  • To read your note, hold it up to a lamp to heat it, or (if you have an adult to help) iron it carefully

Write an invisible note to a member of your family and tell them (secretly) how they can read it…


You can easily send a secret message to a family member or friend using an Alphabet Code! In an alphabet code, you create a CIPHER KEY that only you and the person receiving the note knows about, and write your note according to that key. The alphabet normally looks like this:


If I decide that my cipher key is ‘Move all letters one space to the right’, it will look like this (normal alphabet on top, cipher key beneath):


So if I wanted to use the word ‘CAT’ in my coded message, I would write ‘DBU’ because in my chosen cipher key: D represents C, B represents A and U represents T.

Try writing a message to a family member or friend using your own alphabet code!

  • Decide on your cipher key…the one above is ‘1 Right’ as every letter has been moved one box to the right. Tell the person who is going to receive your letter what your cipher key is!
  • Write out the alphabet with your cipher key underneath it
  • Write your note normally (but remember to destroy it afterwards!)
  • Replace each letter with the equivalent letter in your cipher key
  • Send the note – it will look like gibberish – to your family member or friend!
  • Get them to de-code it and send it back to you in normal English…see if they manage it (and that you used the cipher key correctly!)

Write an alphabet coded note to a member of your family or friend and give them the cipher key so they can read it…


You can also send secret messages using Morse code, which is a code of sounds! There are two basic sounds – a short one (dit) and a longer one (dah). Every letter of the alphabet is represented by a different combination of dits and dahs:

Here is how you learn Morse Code

Sadie taught us about one of the most common Morse codes – S.O.S. (Dit dit dit / Dah dah dah / Dit dit dit), which is an abbreviation for Save Our Souls – a message often sent by ships if they are in trouble.

Why not have some fun typing letters and words into this website to hear what they sound like in Morse code: http://tetration.xyz/MorsePy/.

Try communicating a message to a family member or friend using Morse code! You can say ‘dit’ and ‘dah’ or you could use a musical instrument!

  • Decide what you want to say
  • Write your note normally but with wide spacing (and remember to destroy it afterwards!)
  • Write out the dits and dahs underneath each letter
  • Record yourself doing the whole message in Morse (slowly!)
  • Send the recording to your family member or friend!
  • Get them to de-code it and send it back to you in normal English…see if they manage it (and that you made all the sounds correctly!)

Record a short Morse code note to a member of your family or friend, show them the Morse code alphabet above and get them to send it back to you in English…


You can also send secret number messages using Binary code, which is the language that makes all computers work! There are only two numbers used in Binary – 0s and 1s – and they tell us how many ‘sets’ of numbers are being used. The first seven sets are:


Each set (after 1) is 2 x the previous set (4 is 2 x 2, 8 is 2 x 4, etc.) so the next set after 32 would be 64 (2 x 32), and the one after that…128 (2 x 64).

In this example, the number 4 would be represented as 0001000, because there are no 32s, no 16s, no 8s, one 4, no 2s, no 1s, no 0s.

12 would be represented as 0011000, because 12 is made up of one 8 and one 4.

3 would be represented as 0000110 because 3 is made up of one 2 and one 1.

11 would be represented as 0010110 because 11 is made up of one 8, one 2 and one 1!

Work out some more numbers – maybe your age or your house/flat number…even your birthday (at least day and month, year might be a bit tricky)!

Write a number code to a member of your family or friend and tell them how Binary code works so they can read it…

If you enjoyed Spy School and for more homeschooling lessons visit our free resources page and for homeschooling videos see Minerva Tutors TV

If you do any of these projects, write in to show us at lawrence@minervatutors.com!

Meet Our New Online School!

If you’re thinking of schooling your child at home, then our brand new, thriving online school could be the perfect solution.

  • All lessons and learning material supplied
  • Group lessons with other pupils
  • 1-2-1 mentoring
  • Suitable for pupils in Years 9 & 10 (GCSE)
  • Free trial period available
  • Rolling monthly payments, cancel anytime

All you need is a computer with an active internet connection, and we’ll do the rest. Visit Minerva’s Virtual Academy now to register for an immediate start!

>> Go! <<