The point of school is not to produce geniuses, but to take a mass of illiterates and turn them into semi-literate persons, also giving them time to mature as human beings before they are allowed into university or work. If an 18 year old person can read, write, use basic math operations, know a few facts about the country they live in and speak in a way that doesn't require their fellow countrymen to use subtitles, we can call it a success. If they can say what time is it in a foreign language, they will end up in the school hall of fame.
As a plus, school may introduce people to topics that may interest them and then allow them to find their way in life: from playing an instrument, to gymnastics, to computer programming.
Grades are a fixation of the school system and of all those involved, but they don't measure knowledge accurately. Some companies may not hire you if you have low marks or studied in a less than prestigious school/university, but that has not necessarily anything to do with knowledge and is likely to have something to do with class segregation. So there's a point in making them up.
Vandalism being tolerated is instead a very serious issue the school should address.