I know "school" in the phrase "school of fish" is a collective noun. Is it a collective noun in "school of thoughts" as well?
1 Answer
No, a school of thought (singular thought) is a particular line of thinking, unified by style or approach. From Forced Justice: School Desegregation and the Law by D J Armor:
One school of thought maintains that mandatory techniques are most effective for student desegregation, which is generally defined as racial balance and measured by the index of dissimilarity.
That is, one way of thinking was that mandatory rules would solve segregation in the US. The opposing school of thought espoused voluntary programs.