The number of families applying to city charter schools through an online system designed to ease the admissions process doubled this year, according to the New York City Charter School Center.

This was the second year that the Common Online Charter Application, which the charter center developed, was open to all charter schools for use. The application deadline was April 1.

The number of individual students who submitted the common application rose from 7,130 last year to 15,805 this year. Together, they submitted 58,117 applications, more than three times as many as last year, meaning that the average applicant applied to more schools this year. A total of 145 schools, up from 110 last year, accepted the common application. (Many schools also had their own applications, so the number of common applicants does not reflect all charter school applicants this year.)

In offering a common application, the charter center is responding to criticism that having to fill out multiple schools’ applications discourages all but the most motivated parents and effectively screens out needy students. The common application also enables families to apply easily to multiple schools — a data point the charter sector points to as evidence that the public wants more charter schools.

But most of all, the common application is meant to make the application process easier for families, said James Merriman, CEO of the charter center.

“The easier you make it for people to choose, the better it will be for them,” he said. “The common app is an essential infrastructure you have to build when you have a choice system.”

Merriman said center had helped increase the number of common applications this year by promoting the option widely.

“We spent a lot of time increasing outreach and we got better about who we needed to outreach to,” he said, adding that the center had especially focused on black and Hispanic communities through radio and Spanish-language media.

Under increasing pressure to enroll more students with special needs and English language learners, some charter schools have changed their admissions policies to give those students preference. Daniel Hayman, a policy analyst at the charter center, said schools using the common application offered those preferences at a higher rate this year, and applicants identified as ELLs or as requiring special education services more often, too.

Of the 44 schools that did not offer the common application, 20 belonged to Success Academy Charter Schools —  the city’s largest network of charter schools.

Success Academy’s elementary schools received applications from 12,266 families who applied for nearly 2,500 seats — or five applicants for every open seat, the network announced last week. Success is adding six schools to its network this fall.

Merriman would not comment on why Success did not use the common application. But he said high-performing charter schools can do almost no outreach at all and still receive thousands of applications.

Jenny Sedlis, a Success Academy spokeswoman, said in an e-mailed statement that the network opted out for simplicity’s sake.

“Our enrollment process is a huge undertaking that we seek to make as efficient as possible,” Sedlis said. “We may consider participating in the common online application in future years, but for this year, we needed to reduce complexity. We believe we have accomplished the goal of all charters to reach as many families as possible and make it easy for them to apply.”

Other schools that chose not to use the common application included the six schools in the New Visions network, which are among a tiny number of charter high schools in the city. Others serve specific types of student, such as students who are overage and under-credited for their grades or who are homeless or in foster care, so it doesn’t make sense for them to use the common application, Merriman said.

Because many charter schools continued to offer their own applications as well, the common application numbers do not fully show how many students applied to city charter schools this year. The total number of applications, which are expected to be released at the end of the month, combined with lottery results, will provide a more complete picture of demand for the city’s charter schools. Merriman said most schools have had their lotteries at this point, but some won’t hold lotteries until May.