If 9 out of 100 middle school students are on the track team, and there are 600 students in the school, we can set up a proportion to find the expected number of students on the track team:
9/100 = x/600
To solve for x, we can cross-multiply:
100x = 9 * 600
100x = 5400
x = 5400 / 100
x = 54
We would expect $\boxed{54}$ students to be on the track team.