When the Walton Family Foundation first began to make investments to improve American education in the early 1990s, the idea that our nation could transform how we educate America’s most disadvantaged students seemed next to impossible. In the subsequent two decades, however, teachers and other inspiring educators have shown us that students from tough backgrounds can achieve success in high school, college and careers.

Seeing what’s possible has compelled us to invest with increased urgency.

We are moving forward after reflecting on the lessons we have learned from investing more than $1 billion in American education over the past two decades. We asked ourselves some tough questions, and we expect that the lessons we continue to learn by answering them will guide our giving strategy through 2020.

Lesson 1: All students can succeed, but we still need to do a better job of ensuring variety in high-quality educational options.

There’s ample evidence that even the most high-needs students can thrive — and there’s no need to “solve” persistent, intergenerational poverty before providing high-quality educational opportunities. Nearly 90 percent of KIPP students, for example, come from disadvantaged families. But KIPP’s alumni are graduating from college at nearly four times the national average for low-income students.

Still, there are questions that we must confront. While many “no excuses” charter schools have demonstrated success, how do we reach many more disadvantaged students with diverse needs, including those with special needs and those still learning English? How do we build and maintain pedagogical variety? How do we promote robust educational programs that prepare students to succeed in college, while also supporting and validating other career pathways?

Lesson 2: School choice works, but there must be a favorable policy environment for choice to be truly effective.

From the start of our investment in K-12 education, the Walton Family Foundation has been guided by a simple but powerful theory of change: when families have the opportunity to choose among high-quality schools, children benefit, and when high-quality opportunities play out at scale, the whole education ecosystem grows stronger.

In many places where the Foundation invests — from Washington, D.C. to New Orleans to Denver — choice has helped families and has catalyzed citywide improvements. We’ve witnessed improvements to teacher development and evaluation, the creation of new school choices, and a move toward greater transparency for parents.

But we’ve also learned that availability of school choice alone isn’t enough. There are cities where schools of choice are serving individual students well but not catalyzing system-wide gains.

We must consider: What additional policies need to be in place to create fully functioning choice systems? How do we preserve the policy advances and support implementation so that the promise of new policies result in positive impacts for students? And how do we better support communities in solving local problems?

Lesson 3: Increasing the pipeline of teachers through groups like Teach For America has helped to supply and support new talent for public schools, but we need to do more.

Teach for America (TFA) has helped to build a new generation of teachers, and a new generation of education leaders and reformers. Study after study has validated the positive impacts of TFA teachers in classrooms, particularly in math.

The enormous success that TFA has achieved in identifying and cultivating talented teachers and education leaders would have been unimaginable when the first TFA corps was formed 24 years ago. As we continue to support TFA, it’s a moment for fresh thinking on how we cultivate the talent our nation needs to lead classrooms, schools and the education sector as a whole in the coming decades.

We must consider: How do we source the next generation of great educators? How do we support and retain the great teachers who are already transforming students’ lives in classrooms today?

With a mix of urgency and patience — and with these lessons in hand — we will charge forward over the next five years.

Improving educational opportunity is hard work. It seems that all too often, we move two steps forward and one step back. We cannot ignore a dense web of complexity and a sobering set of challenges, but we see clear reason for optimism and for investing with even greater urgency.

This article originally appeared on Skoll World Forum.