CHICAGO (CBS) — First, the Chicago Teachers Union demanded more makeup days for time spent on the picket line – and they got some of them, exactly as they wanted.

But now, CBS 2 Political Investigator Dana Kozlov has learned that teachers won’t be at work anyway on many of those days – and the Chicago Public Schools system is scrambling to find substitutes.

The Chicago Teachers Union did not budge during its 11-day strike.

“We should return to work in the schools pending one thing – and that one thing is a return-to-work agreement,” CTU President Jesse Sharkey said on the 11th and last day of the strike on Oct. 31.

The union and Mayor Lori Lightfoot agreed to make up five instructional days. But now, not three weeks later, Pritzker Elementary School’s assistant principal sent a letter to parents about the Nov. 27, Jan. 2, and Jan. 3 makeup days, stating, “We anticipate a need or substitutes to cover the classes of teachers who have made advance plans for those days and will not be in attendance in school.”

The letter called on parents themselves to step in as substitute teachers. And principals say it is happening district-wide.

Kozlov asked Sharkey about all this.

Dana Kozlov’s Full Interview With Jesse Sharkey:

“My response is basically that strikes are incredibly inconvenient,” Sharkey said outside CTU’s board meeting.

Sharkey continued: “It’s hard scheduling makeup days. That’s one of those things that happens. Someone whose daughter is being married in Tel Aviv and it’s been planned for two years – and what, are they going to miss their daughter’s wedding? No. And so this is an actual difficulty, and I don’t really know what else to say other than, this is part of what happens when we make up days after a strike.”

Kozlov: “Don’t some teachers have a responsibility – barring a wedding or something – to cancel their vacation and go and teach the classes that they’re supposed to teach?” Kozlov said.

Sharkey: “Well, I don’t control school attendance policy and things like that, nor do I control individual teachers.”

Kozlov: “Some would say CTU held the district and parents hostage to get the makeup days, and now an inordinate amount of teachers are going to miss three of the five of them, and that raises concerns – no?”

Sharkey: “You’re the only person I’ve heard say we held the district hostage.”

But students are required to go to school on those makeup days. Principals are concerns that substitutes will prompt parents to keep their kids home – and low attendance could impact a school’s rating.

Sharkey said school ratings were indeed a CTU concern.

Those attendance numbers count toward a school’s overall year-end rating, unless the board votes to change that.

CPS teachers get three paid, personal days a year.

In a statement CPS spokeswoman Emily Bolton said: “As part of the agreement to end the CTU strike, CPS committed to making up five days and we greatly appreciate the flexibility of principals and families during the strike and through the makeup days. Teachers and staff are expected to work on those days unless they have benefit days available and the day off has been approved by their principal.”