All charter schools are not created equal. That’s according to a new study published by Stanford University research group CREDO, which shows some New York City charter school networks are better than others at improving their students’ math and reading test scores relative to surrounding traditional public schools.

The results are part of a broader study released this month that analyzed hundreds of charter schools and networks across 26 states to assess which types of charters are most effective in boosting student learning.

Most notably, the study found that charter school management organizations (CMOs), which CREDO defines as agencies that hold and oversee the operation of at least three charters, perform better than both traditional public schools and charters not aligned with CMOs. Academic growth was defined in the study as the change in a student’s scores from one testing period to the next.

Nationwide, students at CMO-operated charters received an equivalent of 17 days of additional schooling in math and reading compared to similar students in traditional public schools. In New York City, those rates were substantially higher, with students receiving the equivalent of 80 extra days of learning in math and 29 days in reading.

In comparison, non-CMO charter schools in New York City saw students grow only an additional 34 days in math and actually decline in reading compared to students at traditional public schools (The non-CMO reading difference was not statistically significant).

Five out of 11 CMOs in the city saw distinctly better results. Success Academy Charter Schools, which recently won the Broad Prize, came out on top, significantly outperforming most other networks in the city. Its students gained the equivalent of 228 days in math and 120 days in reading instruction compared to their peers in nearby traditional public schools.

However, the study only examined 168 students from the large network, a small share of its total enrollment of roughly 14,000 students in New York City. In an email, CREDO’s Lynn Woodworth told Chalkbeat that many Success students were excluded from the study because they couldn’t be matched to similar students in “feeder” district schools since the network takes few students after the initial enrollment period.

Icahn Charter Schools, Achievement First, Uncommon Schools New York City, KIPP New York City and Democracy Prep Public Schools all posted lower rates than Success — but still outperformed nearby district schools and the city’s average for CMOs.

Students at Icahn Charter Schools received the equivalent of 171 additional days of learning in math and 46 days in reading, compared to students at nearby traditional public schools. Achievement First students were close, with 125 extra days of learning in math and 57 in reading. KIPP New York City, Uncommon Schools New York City and Democracy Prep all posted gains equivalent to roughly 100 days in math and 50 days in reading.

Two networks — Lighthouse Academies and Public Preparatory Network, Inc. — performed closer to the city’s CMO average. And the three other CMOs — Ascend Learning, Explore Schools, Inc. and New Visions for Public Schools — performed comparably to nearby traditional public schools.

“At the average, independent charter schools show lower gains for their students than CMOs,” the report found. “Despite the wide range of CMO quality, larger organizations of charter holders have taken advantage of scale to the benefit of their students.”