Could you provide some background, please.
1) Where do you live?
2) In what capacity do you visit schools?
3) Can you provide your source for the US$18,000 cost per student per year?
Where I live (Calgary, AB) the average cost of educating a child in public school K-12 is approximately Can$8,800 per pupil per year, half of the figure you quote (not taking the awful 75% exchange rate into account).
My granddaughter attends an inner-city public school (grade 2) and I visit her school regularly. There are a few boisterous kids in her year, but certainly no "unruly" kids. My granddaughter is ethnic Chinese and her best friend is from India. One other regular playmate is from Quebec and another girl is German-Canadian. There are several Muslim girls in another grade 2 class.
Her grandmother was a public school educator for several decades and she assures me that the education my granddaughter receives is excellent.
US$18,000 per year per child? Are you sure?