Collocations for enrolment - noun

high, low
large (esp. AmE)
total
Total enrolment fell between 1991 and 1997.

open (= not restricted)
college, school, university
an explosion in public school enrollments

student
freshman (AmE), graduate, undergraduate
black, hispanic, minority, etc.

boost, increase

be up, go up, grow, increase, rise
be down, decline, go down, fall

on enrolment
The full fee is payable on enrolment.

enrolment for
Enrolment for engineering courses is low this year.

enrolment in
enrolments in evening classes

enrolment on (esp. BrE)
enrolment on a computer course

Enrolment/enrollment is used after these nouns:
college, student, undergraduate