Hi there! We are going to build a "Reflex contest" to allow your students test their reflexes one against each other. They will have to choose the button that matches the picture on the screen before his schoolmate does it. First student getting 10 points will be the winner! This project uses a medium complex program but almost no additional materials.

Supplies

A computer with acces to Scratch (internet or desktop version)
1 Makey Makey kit
2 pieces of paper where you can write or draw the four different pictures of the game
8 "conductor" buttons (we have used play dough but you can use any other conductive material you want)

Step 1: Building Your Controllers

You will have to build two models, one for each participant. For each controller you will need a piece of paper or cardboard where you can fit the drawings or names of the four pictures you are going to use in your game (we have chosen: strawberry, bananas, tacos and watermelon). Then, paste the conductor button next to it.

Step 2: Code the Program With Scratch

First of all, you need one sprite with four different costumes (strawberry, bananas, tacos and watermelon). Create 2 variables for the player scores and another to help you change the costume. Write a piece of code to change the costume every time a player presses a key and until any of the scores equals 10. Give the "costume variable" a number from 1 to 4 for every costume and make it take a random value (photho 1).
Then, for each value of the "costume variable" change the sprite costume to one of the four you have chosen (strawberry for 1, bananas for 2, tacos for 3 and watermelon for 4) and, while the costume is shown on the screen if the right player button or the left player button is pressed, increase the score. You can see how I did it for the strawberry in photo 2 or you can check the whole project here.
I also added a couple of backgrounds to congrats the winner.
Add some "waits" to avoid the score increasing in more than 1 point for every right answer and, that's it!
Please, note that when one student makes a mistake and chooses a wrong picture, the program changes the photo shown in the screen.

Step 3: Connect Makey Makey

Wire every MakeyMakey button to the key you have chosen to increase points in the Scratch project for every picture. For instance, we have joined the "strawberry" play dough button in the right controller to MakeyMakey "UP" button, and to "A" button in the left controller. Complete the rest of the buttons.