At least for me, this was the most difficult achievement for this game cause, Doctor of Conseling or Vending Machine Tycoon it was possible to acomplish just letting the years pass by, but for this one there are more things to consider.
How to Obtain Abandon School! Achievement
Only one student
First, you don’t need one student per class, that means you just need one student in your all school to try the achievement. You can get that only one by expulsing most of your students (if you have a lawyer) or just letting the years pass by without bringing in anyone new.
You need janitors
If you don’t have janitors, the school it’s gonna get dirty, and that means that you’re only student will get sick, and if that happens it’s a game over cause your school it will be considerer as a pandemic.
The same as before, cause you only have one student, if this become problem, it will be again a game over. To keep this out, it’s better if you ignore the events, you don’t know if the only choice it will develop it’s your student becoming a smoker or a bully.
No vending machine
The school cannot have any way for the students to get food. That way you just have to wait and make the days pass until the student get desmotivated and decided to abandon.
Keep in mind that all this it’s so much easier if you already have a lot of money in that saved, cause your incomes comes from your students, and because you only have one, you may lose the game even before if you get out of cash. Especially if this doesn’t work out in the first try and you have to keep trying another year.