An adventure game is much like a computerized version of "choose your own adventure". They eventually grew to have complex graphics and helped to lead to FPS games (First Person Shooter Games). However, you are to recreate an earlier, kinder, more-appropriate-for-the-school-setting version of the game.
Start your player with a name and a scenario explaining what their goal is (find a magic sword or whatever). The player will then choose where they will go and the program responds to their decisions. If the player chooses to do something that is impossible in that location, they are not allowed to do it. Sometimes there are objects to pick up, things to do and puzzles to solve. You could even add ASCII art pictures.
This is an example:
Welcome.
Please enter your name>> George
You are a gameskeeper in a castle. Today your job is to go
hunting in the woods. You have nothing with you except your bow
and arrows.
You arrive in the forest and pick some berries. You roam far from the castle. As you walk, you notice that it is getting darker. Suddenly you hear a noise behind you. You turn and you see a Goblin. It is not happy to see you. What do you do? (1) Start singing. (2) Throw a fireball. (3) Strike him with lightning. (4) Run away. (5) Shoot an arrow at him. >> 5 You lose! You have no points left in that category.
You continue on your way, passing by some strangly quiet farmhouses. You walk around the farmhouses and you see a huge burned patch of ground. The barn is burning. You look up to the sky and you see a Dragon. It is also not happy to see you. What do you do? (1) Start singing. (2) Throw a fireball. (3) Strike him with lightning. (4) Run away. (5) Shoot an arrow at him. >> 1 The Dragon gets sleepy and flies away.
And whatever.