The pace at which the highest-performing charter-management organizations (CMOs) are "scaling up" is being determined largely by how rapidly they can develop and hire strong leaders and acquire physical space, and by the level of support they receive for growth from city or state policies, say leaders from some charter organizations viewed by advocates as having high student achievement. To explore what might be obstacles to growth for successful charter operators, "Education Week" interviewed leaders of five of the seven CMOs in the NewSchools Venture Fund's portfolio that the fund sees as producing the best student-achievement results. The seven charter operators are: (1) Aspire Public Schools; (2) Achievement First; (3) Green Dot Public Schools; (4) Harlem Success Academy Charter School; (5) the Knowledge Is Power Program; (6) Uncommon Schools; and (7) Rocketship Education. That same set of operators has also been identified by the Center on Reinventing Public Education, at the University of Washington, in Seattle, as the nation's top performers. As might be expected, some of the charter operators identified by charter supporters to have the strongest records in student achievement are focusing their expansion in cities or states that have policies viewed as friendly to charter schools, such as New York City and Newark, New Jersey, and are steering away from locations viewed as unfriendly. Legislation passed in the last year that relaxed limitations or lifted caps on opening charter schools in Illinois, Indiana, North Carolina, and Tennessee also will benefit charter operators that want to expand. Charter schools are publicly financed but largely independent of the regular school system. Some are single-site schools; others are part of growing regional or national networks operated by CMOs. Although federal data show the number of students enrolled in charter schools has more than tripled, growing from 340,000 in 1999-2000 to 1.4 million in 2008-2009, not everyone believes policies encouraging their growth have been fair.