Chicago Public School students returned to school this week, but officials since this summer have been scrambling to fill more than 1,000 teaching positions.

Surprisingly, the greatest need isn’t for math and science teachers, but for physical education, special education and reading teachers, as well as librarians and counselors.

When school started last year, the system had the lowest vacancy rate ever, about 2.5 percent, said Nancy Slavin, head of recruitment and workforce planning for CPS.

But this year, a combination of principal and teacher retirements and the opening of several new schools has created a much higher demand prior to the start of school Sept. 4.

“We have need across the city,” Slavin said. “You have to remember that with 600 schools, if each one needs one (teacher), that’s 600 right there.”

Of the roughly 25,000 CPS teachers, 1,800 retired this summer, in part because of a new pension enhancement program, Slavin said.

CPS also lost about a quarter of its principals – around 150- to retirement this year.

When the exiting principals were recognized at the Chicago Board of Education meeting in June, board President Rufus Williams remarked CPS was seeing “the other side of the Baby Boom.”

Most of those principal spots have been filled; however, individual schools do their own hiring, so a new principal, one who is learning the ropes while trying to pick teachers, can slow the process.

Slavin declined to name the schools in need of the most teachers, but said the vacancies haven’t taken CPS by surprise.

On Aug. 10, CPS held a job fair at Soldier Field to recruit and hire teachers. That job fair, though, was planned more than a year ago.

Slavin likened the job fairs to speed dating, but stressed that teachers are rarely hired on the spot. Instead, they are encouraged to visit the school and interview further with the principal.

“We have teachers that interview at 10 schools, get 10 offers, and choose one. So there’s an empowerment of the teacher,” Slavin said.

The same is true for principals.

Sala Sims, principal of Catalyst Elementary School, a new school located in the Austin neighborhood, said she looked for people who saw teaching as a vocation, not just a job.

With 221 students and a 13-1 student-teacher ratio, Catalyst, Sims said, prides itself on fostering strong relationships between teachers and students.

“It’s really important for us because part of our mission for our school is for our staff to really connect with you,” Sims said. “They have to see it as something where they want to connect with [student’s] families outside of class.”

Overall, CPS has no shortage of teacher applicants.

Slavin said there are more than 15,000 in CPS’ database – it’s just a matter of moving them through the process of paperwork and interviews, and pairing interests with positions.

“Our hiring is almost like a free marketplace,” she joked. “We don’t have a high need in high school social studies, but unfortunately, there are a lot of those [teachers applying].”

There are not, however, enough in other areas.

Under Renaissance 2010, contract schools, such as Catalyst, and performance schools must hire certified teachers. Charter schools on the other hand have more flexibility.

Sims had mostly every position at Catalyst – which was scheduled to open Aug. 27 – was filled this summer, except for one subject: physical education.

“People are interested [but] most of our [applicants] haven’t been certified,” she said.