more students said they didn't like their school

Let’s focus on the underlined part in (1).

(1) And when more students said they didn’t like their school, the percentage of smokers in the student body [color=red]also was higher.

“Also” suggests the same thing applies to something else. In view of this, the part at issue can be paraphrased as “[color=red]the percentage of students who said they didn’t like their school [color=red]was higher.”

Do you agree?
Thank you in advance
Seiichi MYOGA

Okay. Enough. I’m finished.