Public schools usually suck at educating the students because they are funded by tax dollars which pays for the education of the students and pays the students salaries.
Some teachers at public schools become teachers because they really do love to teach and help children and students learn even though they might not get a good salary.
However some teachers at some public schools are only there for a job and are not being paid enough and don't really care about the students education.
So some public schools may suck while others may not suck as bad.
I've had good teachers and bad teachers at public schools before when I was a kid so it can vary from school to school.
Usually a private school that is being paid for directly by the parents is a better school and gives better education because the school is being paid directly by the parents to provide their child a good education.
So those teachers get a better salary and are more motivated at teaching the students properly.
However some private schools could suck just as bad though so it doesn't always mean that you'll get a better education at a private school versus a public school.