The Prince William County school board says hundreds of students learning English as a second language have left in the middle of the academic year.

School board members say the loss of 630 students in the English for Speakers of Other Languages program illustrates that immigrants are leaving after an illegal-immigration crackdown was approved.

School officials say the ESOL population rose by more than 1,500 students in October to about 13,400, but then began to decline. The county's new illegal-immigration policy was approved October 17.

Board of County Supervisors Chairman Corey Stewart says the drop in ESOL students is "the first concrete data" to indicate the county's new policy is working.