Maine’s 2011 charter school law got legislators’ support by setting a cap of 10 schools in the law’s first 10 years. Now supporters of the original measure have come back with a proposal to lift the cap five years sooner than originally planned – but there’s no reason to rush and every reason to proceed deliberately.

Of the roughly 182,000 students in Maine, about 2,000 attend one of the state’s nine existing charter schools. State law permits the chartering of up to 10 schools by 2021 and calls for the Education Department to evaluate the charter school program and issue a report to the Legislature. L.D. 1158, sponsored by state Sen. Garrett Mason, R-Lisbon, would get rid of that limit and open up the approval process to more applicants.

We’ve long supported the introduction of publicly funded charter schools in Maine: They serve young people whose needs aren’t being met in traditional schools, such as those who want to focus on a specific subject or who learn at a pace that’s different from their peers’. But to reach students who have different needs, Maine’s public charters are trying out new and different strategies — some that hit the mark, and some that don’t. The schools are pilot programs, and state evaluation is needed to find out whether they’re working.

Mason himself, who also sponsored the proposal that created charter schools, acknowledged as much when that bill was approved. So has Maine Charter School Commission member John Bird, who said at a May 2 meeting that he’d like to see objective studies on the performance of Maine’s charter schools, of the kind conducted at the Maine Education Policy Research Institute.

The commission has done a good job of screening applications: It hasn’t hesitated to send applicants back to the drawing board before their charters can accept students. But legitimate questions have been raised about the commission’s ability to oversee the performance of the schools it has approved. Education Committee Chairman Tori Kornfield, D-Bangor, voted against the proposal to lift the cap, citing the commission’s decision to support a contract renewal and expansion of a Cornville school where the percentage of students who are proficient in English and math is among the state’s lowest.

The Education Committee’s split on the proposal to lift the charter cap means that supporters could attempt to revive it on the floor. But with the state assessment of Maine’s charter schools due this year, legislators should recognize that they don’t yet have the data they need to make this critical decision — the cap should stay in place until it’s clear that the system is ready to be expanded.