As in society today in the United States Canada, United Kingdom we all require conforming to laws, rules & regulation, and possibly meeting certain standards, such as at work or education grades for future study.
A student that gets expelled or kicked out of private school is mainly a last chance or for serious rule breaking the enrolled student has committed that warrants expulsion.
A fee paying school doesn’t wish to kick a student out as it’s not good for the school or student, but in certain circumstances they’re not left with much option.
Every private school has a set of written rules and policies that each students must agree, normally by signing a student code of conduct document outlining acceptable behavior and consequences of rule breaking actions.
Reasons private schools can kick students out
1. Serious rule breaking student commits or misconduct issue
Persistent truancy from boarding or day school during timetabled teaching hours, basically arriving at school, going to the first lesson and non attendance until lunchtime with a student leaving the school campus without permission.
A private school has a fairly strict set of rules and code off conduct. They are responsible legally for students during school hours and if they can’t control you’re behavior or you refuse to change then they can expel you after written warnings and time to change.
Additionally as an example: A high school student brings drugs, alcohol and a firearm on school grounds, either in possession, dealing or use of them would most likely be kicked out of school immediately, depending on the severity of rule breaking.
2. Violence & physical assault on staff or students
Any student that commits physical violence or assaults another student, teacher or employee at a private school can be expelled from the school immediately.
Schools operate under different legislation & laws and the school can, and will permanently exclude a student that beats up or inflicts physical harm on another student, even if a student suffers from ADHD.
Health & safety of students and others at school is paramount and a private fee paying school, day or boarding will get rid of a violent student rather that take a chance of more occurrences.

3. Damage to school or student property
Using a scenario: John & Jane are high school day students at private school.
They’ve been warned before about graffiti on school walls, although for two days they go around kicking & damaging doors and break 3 large pains of glass causing $9,700 because they’re angry & frustrated.
Written school rules will state students can’t intentionally damage school property and a consequence is that John & Jane can be expelled for such damage to school property and persistent rule breaking.
4. Threatening behavior or verbal abuse towards another person
A student using threatening behavior or abusive language towards others will be warned and or reprimanded for they’re actions. Repeated similar actions could result in a student being kick out of school.
Mild threatening behavior can be classed as bullying where a junior student is picking on another student calling them names or other constant insult or accusations, true or not.
Schools, private or public will not accept bad behavior from any student that’s a bully, and persistent or bad enough instances can result in a student’s expulsion.
5. Student doesn’t fit in or school can’t offer education
For students that don’t fit in at school or are not coping with the required standard of class teaching, understanding and other factors can result in them being asked to leave by a private school education provider.
Students will get all the support & assistance the school can reasonably offer, although they’ll only required to get so far.
A learner that has a disability, such as autism where they’re struggling with education class work and develops needs the school doesn’t have could be asked to leave. The school may not have sufficient teachers with teaching & learning skills or facilities for the student’s educational requirements which may result in the school withdrawing provision for education to that student.
An international student that has difficulty understanding enough instruction in class will ultimately struggle in education standards and other school requirements.

6. Non payment of school tuition fees
All private schools require finance to successfully operate with a large proportion of operating costs paid by parents through tuition fees to the school.
Should a parent or the organization that pays a students school fees stops paying the agreed amount of money the school can, and will rightly stop all teaching & access to the school, and ultimately bar a student from returning.
7. Kicked out of private school for bad grades
Although not all private day & boarding schools, some will have certain written admissions and continuation requirements for students being enrolled at the school. One is meeting a certain standard of overall grades that a student requires otherwise the school will not let you enroll for the following year.
Persistent poor grades can be a school terms & conditions violation that a student occurs. The school will give you plenty of notice, time & assistance to improve, although they can discontinue tuition to a student.
8. Student uses constant disruptive behavior at school
When I was a high school teacher occasionally 1-2 students in class attempted to disrupt the class lessons by showing off or prank another student to get a reaction.
Disruptive behavior distracts the teachers and students in class, and can interrupt the flow of a teacher’s lesson or ultimately stop a lesson for the teacher to reprimand or disciple a student.