Click the four glinting quarters around the room. There's one on the music stand in front of you, one on the drumkit, and two on the floor along the wall. Next, click Phred, the character in the back left corner; in exchange for the dollar, he'll give you a whistle. Click the whistle in your inventory to use it, allowing you to leave the classroom.

In the hall, click the arrow pointing to Mrs Sleep's classroom to enter it.

Click the desk with the slightly open lid; you'll find some trombone slide oil and 30 cents.

Leave the room and go right.

Click the 1st locker on the right: the one with 2 slits instead of 3: to find 10 cents.

Go right.

Click the slide oil in your inventory to open the rusty vent. Take the toilet paper, then enter the Teacher's Lounge.

Your dialogue choice does not matter, as you'll be kicked out regardless of what you pick. However, you need to do visit the teacher's lounge in order to progress.

Back in the hall, go left and enter the men's room.

Click the toilet paper to give it to the student. Take the mop after they've gone and leave.

Enter Mr Sum's classroom.

Click the papers on the desk to find another quarter, then leave.

Back in the hall, go left and into the Janitor's Closet.

Click the mop in your inventory to return it. You'll receive 5 cents as a reward.

Go back to the teacher's lounge, which will now be empty.

Click the back of the vending machine.

Click the plug to power it on, then use the vending machine to receive a cookie.

Go back into the hall and give the cookie to Chubb to get him to move from the door, the enter.

Click the door to Mr. Mister's office.

After the cutscene, return to the hall, then go left 3 times to unlock the doors and escape from school, ending the game.