Since Governor Bevin’s election, the discussion about public charter schools has ratcheted up several notches. Kentucky’s new governor publicly supports charter schools as one tool that can help boost the currently lagging performance in the state’s public school system, especially for minority students.

Still, anti-charter sentiment from adults in our existing education establishment remains strident, with people throwing all sorts of data around claiming that charter schools really don’t perform well.

While much of this is political “noise,” we do see some important evidence in a series of reports from The Center for Research on Education Outcomes (CREDO) at Stanford University that charter-school students nationwide are pulling away from their traditional public-school counterparts. Furthermore, this finding helps explain why a lot of reporting on charter schools doesn’t get the analysis right, treating charters unfairly in the process.

CREDO’s reports show that it takes time for charter school students to get turned around and on track. Per CREDO, more than a year is required before charters accomplish this important transformation.

For example, this graph comes from CREDO’s latest “nationwide” charter study from 2013.

This graph tells a rather remarkable tale.

In this graph, performance of traditional public school students is shown by the horizontal axis (marked as the zero line). Charter student performance is plotted relative to this line. Let’s explore what is shown in this CREDO graph.

According to CREDO, students who have only spent one year in their new charter school perform well below the performance for comparable students in the traditional system. In math, for example, the first-year charter students lag behind traditional public school peers by about 58 days of learning and in reading first-year charter students lag by about 43 days of learning.

But, is that lag really a reflection of charter performance or more a residual effect because charter students often enter their new school several years behind grade level? For example, the KIPP Academy schools reports

“Most students enter KIPP as fifth-graders performing well below grade level in reading and math.”

The US Department of Education has also examined charter schools that are working well, saying they “work with many children who enter school performing far below grade level and who are from neighborhoods and families with scant resources.”

Given that many charter students come to their new school well behind, it is no surprise that CREDO finds students who have only spent one year in charters are still notably behind. The new charter students simply have not been in the charter school long enough to fully benefit.

But, notice what the CREDO graph shows for students who spend more time in charters.

By the time a student has spent two years in a charter school, he or she has already moved ahead of their traditional public school counterparts by an equivalent of several weeks of learning in both reading and math.

Even more remarkable – across the country, on average – by the time students spend four or more years in charters, they are really out in front of their traditional public school counterparts. In math the charter students have about an equivalent of 43 extra days of learning in math and 50 days in reading.

Things look even better when we look at states with stronger charter school programs. When CREDO examined the above average charter system in Louisiana in 2013, the researchers found that by the time students spend four or five years in the Louisiana charter system, they generally outperform traditional public school peers by about 180 days of learning in both reading and math. That is the equivalent of a full extra year of schooling.

CREDO found similar results in another report on New York City’s charters. In math, by year four, the benefit of going to a Big Apple charter school worked out to about 216 extra days of learning once you apply the scales used in the Louisiana report.

So, one remarkable lesson to be learned from CREDO’s graph above is that charters need some time with students before the better performance of these schools of choice becomes obvious. However, once students spend sufficient time in charters, generally two or more years according to the graph above, the benefits start to become notable. This becomes rather dramatically true in better-run charter programs like Louisiana’s.

There is another important take-away from the graph. Any report on charter schools that lumps all charter students together, including first-year students, won’t fairly reflect what charters are capable of producing. This fact of life explains why a number of reports don’t show much if any advantage for charter schools.

As a note, CREDO isn’t the only group that has examined the impact of charters on students over time. A 2009 study by the Boston Foundation also found that students who spent more time in Boston Massachusetts’ charters did progressively better over time compared to their traditional public school counterparts.

If a schooling model can take kids who are notably behind and move them a year or more ahead of their counterparts in the traditional schools, it is time to bring that important educational tool to Kentucky. Many of the Bluegrass State’s students are underperforming and could use the boost that well-run charter school programs are providing across the country and in major cities like New York City and Boston. It is irresponsible not to offer our students this option.