Every year, school districts welcome -- and then lose -- thousands of promising new teachers. For too many, the job is overwhelming. How can we improve instruction and reduce teacher turnover -- especially with limited resources, in our highest-needs schools? In the "Growing Great Teachers" report, we use research-based "impact modeling" to show how a strategic approach to recruiting and supporting rookie teachers could yield as much as 4.2 extra months of student learning. We provide 5 recommendations for school systems to leverage their investment in structures that provide rookie teachers with both shelter and development.