Her job was described as “high-stakes” and “daunting.” But leading New York City’s massive, breakneck effort to make universal pre-K a reality was nothing short of a dream for Sophia Pappas.

Pappas was head of the Department of Education’s Office of Early Childhood Education when Mayor Bill de Blasio was elected — partially on the promise of free, universal access to preschool. The mayor wasted no time in getting the program off the ground.

“Knowing that this is a really critical and unique time in a child’s development, I was thrilled with the ambitious timeline,” Pappas said. “Because a kid is not going to get that year back.”

A little more than three years later, the number of students in pre-K has tripled to more than 70,000 and the program is highly popular with parents. Not bad for someone who, like many young teachers, struggled with classroom management and was fired from her first teaching job in Newark, New Jersey.

Now, after leading an expansion effort that has been watched across the country, Pappas is moving on.

To what and where, the 35-year-old Georgetown and Harvard grad — who also led early childhood efforts with Teach For America — isn’t yet sure. She expects to wrap up her tenure this month.

On her way out, Chalkbeat spoke with Pappas about her role in the city’s historic effort. Here’s why she says “joyful learning” isn’t an either-or proposition and what motivates her to get out of bed.

A former pre-K teacher herself, Pappas also shared some departing tips for pre-K teachers:

“Be comfortable with being uncomfortable. Stick with it. Just bring it for your kids and families every day,” she said. “And crouch down, at eye level, to meet the kids where they are — for every one of them when they enter the door.”

This interview has been edited for length and clarity.

Implementing universal pre-K in the country’s largest school system is quite an undertaking. Did you have any anxiety about it?

Remember, I came in before de Blasio was here. But when the mayor came in and his number one priority was making high-quality, full-day pre-K available to all 4-year-olds, this was like a dream for me.

As an early childhood educator, and somebody who deeply believes in the importance of high-quality, full-day pre-K, having a mayor who’s setting a clear vision and sort of leading the charge for us to make this a reality was just incredible. And so, while yes, it seemed like a really big task, I had a lot of support.

What did you think about the speedy ramp-up? Did it seem impossible?

Having been a pre-K teacher who saw first-hand how important this year was for kids and knowing that this is a really critical and unique time in a child’s development, I was thrilled with the ambitious timeline. Because a kid is not going to get that year back. So being able to do this quickly, while really focusing on building both access and quality at the same time, was very appealing to me.

I knew it would be a big job but I also knew at every step of the way, even at the beginning, that we had the strong support and leadership from the mayor to the chancellor and so forth.

The city opted to work with many private early education providers — about 60% of the programs are in private centers. What challenges or opportunities did that present?

I think we have incredible opportunities in this city to both offer families a unified system of pre-K that’s going to deliver on quality — whatever door a child is entering through — and to have diverse options for families in different settings. And so one way that we do that is through community-based partnerships.

From the beginning of expansion, our community-based providers — whether we were already working with them as half-day programs or programs that maybe were providing early childhood services privately — really stepped it up and responded to the mayor’s call by applying through our rigorous application process.

Schools Chancellor Carmen Fariña has talked about the importance of making pre-K fun and joyful, but this initiative is also a way to set kids up for success in school. How do you balance that?

I don’t think it’s a choice you have to make, ‘either-or.’ It’s not joyful or setting a foundation. You set a foundation for children by having a fun and joyful environment where there is a lot of play, which is just how young children learn. It happens to also be what gets kids excited about learning, which is a really great benefit and outcome of pre-K.

So a lot of our work has been focused on — in our professional development, in the standards we set, in the curriculum units that we created — showing programs how you teach various skills through play. That goes for our community-based centers. That goes through our schools and for us, that’s really the focus.

Now that we’re a couple of years in, how should we be judging whether pre-K has paid off the way the city hoped it would?

When we first made this happen and rolled out all the programs, there was a lot of effort put into making sure families knew how to enroll and had support in that process. So the fact that we are now at nearly 70,000 kids who are enrolled, up from 20,000 when we started, I think is a really important marker of success and we should continue to look at enrollment in the program.

The other big way is, we were — in the beginning especially — doing a lot of work to make sure we had enough programs to provide pre-K in our schools and our community-based centers. And in both of those cases, they went through rigorous processes to even become pre-K providers. So the number of pre-K providers we have year after year running pre-K is also a marker of success.

The other way is we look very closely at what’s actually happening in the program. So looking at the quality of the learning environment and the interactions happening, to really make the most of this opportunity for kids ,is something that we monitor with two valid and reliable assessments. And we recently reported out, and did this last year as well, how we’re doing on those measures.

Quality has improved over time, but there are still some schools and centers deemed ineffective under the assessments the department uses. What is the city doing about that?

As you can imagine, in any big system you’re going to have programs with different strengths and things that they’re working on. Our focus is on working with each program, based on things that are going well and things that they need to work on, to provide support. We do that through a few different strategies.

One is, there’s ongoing professional learning — not just for the teachers but also for the leaders of the program. So this is teaching teams — lead teachers and assistants — and the administrators. That’s really important because we know what happens in the classroom day-to-day is important and we also know the leaders of that program, in their ongoing work with their teachers, need training and support. So that’s one way.

The other way is we have a dedicated team of 100 instructional coaches and 125 social workers who are regularly going out to sites to provide direct coaching.

Both of those things are happening throughout the school year and we really home in on what each program needs to continue to move forward.

What about as kids enter and progress through school? Will they be taking specific assessments? How will you measure whether they’ve made gains because of pre-K?

There may be other places in the country where they have a kindergarten entry assessment. We are not using that here in New York City. I think we always have to balance having ways of looking at progress and being mindful of what is developmentally appropriate for young children.

You taught pre-K yourself. How did that affect your approach to the work?

Teaching pre-K just showed me firsthand how important high quality pre-K is. I taught in Newark, New Jersey, in a school-based pre-K program. My kids came in with a wide variety of skills, and over the course of a year, grew a lot. That was through play-based learning.

I also saw how important partnering with families from the beginning is … I would say that had a lot to do with how we’ve approached the work here. When we talk about program quality, we talk about both classroom instruction and family engagement.

The experiences that I had as a teacher and my memories of my children and their families really are what get me up in the morning, because I had that direct experience. And in this job I’ve had the fortune of impacting thousands of children.

What’s next for you?

I am committed to staying in early childhood education because I’m so passionate about it. It’s where my heart is. I’ve also seen, through the Pre-K for All experience, what’s possible when you have strong leadership coming from the top and everyone working together to make something happen.