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Shake the plant in front of the door. A key will fall out (3/3). Pick up the KEY and use it on the front door. Enter the school (5/8). The door locks behind you.
Take the PICTURE from the wall. One corner of the rug is folded. Pick up the corner and find a key under it. Pick up the KEY (5/13) . Enter the toilets on the left.
Look in the bin. There’s a KNIFE pick it up (5/18). Use the knife on the picture and find another KEY. Use the key to unlock the door of the Biology Classroom (5/23).
Enter the room. Take the piece of PAPER from the teachers desk (5/28). Read the paper telling you that Jan had some spare keys and hid them around the school. Open the cupboard and take the BRICK with you (5/33). Use the grey key on the box and take the SNAIL out (5/38). Leave the room and go to the maths room.
There’s something hidden under one of the desks. It’s a pair of SCISSORS. Take them (5/43). Look at the blackboard and the message there. Use the brick on the window and go through them (5/48).
Pick up the brick again. Talk to the janitor. It’s Jan! You can have the chalk and the rake but need to do something in return. For the chalk it will be the strip of leather, for the rake it will be the snail. Give the snail to Jan. You receive the RAKE in return (5/53).
Use the rake on the leaves in the corner. There’s another KEY. Pick it up (5/58). Use the key on the door next to the leaves. You can go home now (10/68).
Game source: A copy of the game was found here  on the internet.