Julian High School student Donzell Chester learned a harsh math lesson last year: Too many kids, not enough teachers. That added up to 62 kids in his freshman algebra class.

DONZELL: People had to stand up. People was on the floor writing, it was that packed. 

Every year, the district predicts how many students will show up to each of its schools. And it assigns teachers based on that prediction. 

Then, the kids arrive.

At Julian, 240 extra students showed up—the school was short 8 teachers. It was a similar story at Robeson High School, where students like Lorraine Walker and Jasmine Knight had a full schedule of substitutes. Here they are on October 7 of last year, 6 weeks into the school year.

LORRAINE: We’re really just coming here to sit here and play around. There’s really not even no point to come to English.  JASMINE: We have substitutes every day. And then they expect us take the three-week test, and we ain’t had no teachers that taught us nothing.

Principals and teachers are also frustrated. Senn High School math teacher Jesse Sharkey says the chaos comes at exactly the wrong time.

SHARKEY: It’s really hard in the beginning of the year to establish the right kind of rapport with kids when your class is bursting at the seams.

Enrollment can change dramatically—both up and down—at neighborhood high schools at the beginning of the year. So CPS traditionally waits until the 20^th day of school for an official head count, then authorizes schools to hire more teachers.

It’s partly about money. Interim budget director Christina Herzog:

HERZOG: When we’re as tight as we are, every dollar does count, so we like to be as precise as possible, and as responsible as possible financially. 

It’s also about fairness, district leaders say. They can’t give a school a greater allotment of teachers when the students aren’t there.

But last year, CPS had to round up 78 teachers weeks into the school year because its projections were off. Officials admit they underestimated enrollment by at least 50 kids at 19 high schools. That said, Ron Huberman promises kids won't lose weeks of instruction this year. This is his first September as head of CPS.

HUBERMAN: We’re going to authorize adding teachers within the first week of school where we see additional enrollment, which we believe will help solve a significant part of this problem.

The district looks at past enrollment trends to predict a school’s future enrollment.

DISPENSA I’m Jimm Dispensa. I’m responsible for projecting all schools’ enrollments, every year.

It sounds crazy, but Chicago never requires eighth graders to say where they’re going to high school. So Dispensa has to guess. And that’s getting harder… new high schools are opening every year in Chicago.  

Some think the solution lies in the distirct’s magnet school model, where Dispensa’s projections are almost always spot on. That’s because kids apply there, and enroll early.

DISPENSA: We need to find ways to engage communities and families particularly at the neighborhood high schools, so that we know up front in the spring how many students are projected or registered to go to a given neighborhood high school.

That’s what many other large urban districts do.

In Chicago, bad enrollment projections are derailing other efforts to improve struggling high schools.

Robeson last year had extra money and staff to keep freshmen engaged in school —but many ninth graders didn’t even have teachers…. they weren’t engaged at all.

BERRY: The more problems you have in schools like that—it compounds.

Clarice Berry is head of the principal’s association.

BERRY: Those are schools that they should go in and make sure that they have everything they need. Because those are the most fragile schools in the system.

Donzell Chester, the kid who found himself in an algebra class of 62 kids at Julian, has to repeat algebra this year.

DONZELL: Only three or four people passed. They were the smart ones who were able to focus. Everybody else flunked the first semester.

Today, CPS is deploying teams of long-term substitutes to some 20 schools it thinks might get extra kids. Huberman says principals who think they’ll be hit should have potential hires lined up. But it’s not a good time of year to be hiring. Most believe the best teachers have already been snatched up.

 Last year, CPS underestimated enrollment by at least 50 students in 19 of its 116 high schools. In overenrolled schools, students were assigned to overcrowded classrooms or given substitute teachers--sometimes for weeks--until the district authorized the schools to hire extra teachers.