Game narrative. The parity check activity serves for children to approach key questions on computing:

• Why is it important for computers to be able to detect if the data received is the same as the data sent?

• What if I sent you an email that said you could now have Monday off school, but when you received it, there was some electrical interference and a bit was changed from off to on so that the word "now" became "not". What would your reaction be?

• Can computers correct these sorts of mistakes automatically, and how would they do that?

To be able to understand how to detect and correct errors, we use the parity check. By definition of Technopedia, a parity check is: "the process that ensures accurate data transmission between nodes during communication. A parity bit is appended to the original data bits to create an even or odd bit number". In our unplugged quest version, we have decided to make children detect errors in key messages and to open discussion on additional topics if the teachers want.

Game rules: To understand error detection, we will use grids drawn on any material you want - on a whiteboard, on paper, or printed thanks to the material given in the printables section. Grids are composed of white squares (being filled in with letters in our case but you can also put numbers, images, or left them blank), on which the teachers or the pupils themselves can draw a pattern, using black cards (colouring directly on the whiteboard in black, cutting small pieces of coloured paper, using magnets ...). In our case, the black cards are used to display a sentence among a grid of letters or you can also use them to perform pixel art for instance. Once the pattern composed of the black cards will be defined, the person in charge of designing the grid will secretly add one last column and one last line acting as our parity bit to each row and column. If you have an odd number of black cards in a row, you add another black card to the row in the parity bit column; if you have an even number of black cards in the row, left the parity bit column in white, to keep it as an even number. Perform the same work column per column and put this information in the final parity bit row. Once this work is done, still in secret, within the patterns, introduce an error (either adding or removing a black card) to the grid without changing the parity bit. The game starts here, up to your pupils to find back, performing a parity check, which card has been moved, added or removed to reveal the correct information by comparing, row by row and column by column, the number of black cards with the parity bit information.

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Game settings options in the framework of the Unplugged Quest:

• Option 1. Every group / individual player discovers one word of the message and then the whole class come together and arranges the message in the correct order. This already warms them up for contemplating the societal challenge, posed by the message. The teacher guides the process of finding the right word order, mitigating the discussions and giving directions. Once the message is discovered the teacher starts an open discussion, providing students with some important information on the topic.

• Option 2. Every group / individual player discovers one full message. The messages are interrelated and disclose different aspects of a modern challenge. The class gathers together and presents the messages they have found. Each group interprets the message they have and then the whole class tries to make the connections between the problems. The teacher moderates the whole process by giving guiding questions and explaining general aspects of the problem.

Playing the game in the classroom step by step:

• In the full classroom, the teacher explains how parity check works on a simple grid display on the whiteboard and explains how work the parity bit column and row. The teacher can use a grid with one word, or the pattern grid given above. Teachers can also follow the steps presented in the CS Unplugged activity as an introduction (available here: https://www.csunplugged.org/en/topics/error-detection-and-correction/unit-plan/parity-magic/)

• The teacher describes in a nutshell general aspects of the information transmission and why error detecting is important and helpful in verifying given information.

• Once the logic behind parity check is well understood by students, the teacher splits the class into small groups of 2/3 pupils or individually.

• The teacher distributes pre-prepared mistaken grids.

• In groups (or individually), students in their role of reporters find and correct the error in the grids they are provided.

• Once the information is discovered, the whole classroom gets back together to present their word/message.

• Students discuss the strategies used to achieve the results. This way, self-reflection and metacognition are promoted and strategies that can be applied to other contexts are evidenced.

• The teacher starts and moderates an open discussion on the topic of the hidden message(s).

• After students have warmed up, they can try with girds containing more than one mistake per grid.

Role of the teacher and game organisation:

• The teacher explains the principles behind parity check on a simple grid (adding a row and a column with the parity information).

• The teacher describes the principles of information transmission and error detection and its application in modern world.

• The teacher supports the process of error correction in the groups (or individually).

• The teacher receives the groups'(the individuals') grids and moderates their presentations in class.

• The teacher provides general information on the topic of the discovered message(s) and moderates open discussions