With the end of the school term just days away for most students, opponents of Wake County’s new student assignment plan made last-ditch attempts Tuesday to engineer changes to the plan for the 2013 school year.

Objections to the plan focused partly on the problems families are having in securing the school they want for their children, and partly on critics’ views that the plan will diminish the magnet school program and create more schools with high concentrations of low-income and minority students.

Superintendent Tony Tata has said that a large majority of Wake families are pleased with their students’ assignment under the plan.

In response to demand from families dissatisfied with their assignments for next year, board members voted Tuesday to give thousands of families who are on waiting lists under the choice-based plan until July 18 to determine whether their students will find a place in their first-choice schools.

During an extended public-comment period, several speakers expressed concern that low-income students and those from minority groups would gradually be isolated in certain schools under the choice plan, which does not take diversity into account in deciding school assignments.

“I believe that we do have a pro-integration constituency in Wake County,” said Robert Siegel, who spoke during a public comment period.

Their arguments found potential fuel in school-by-school estimates released Tuesday of changes in income and ethnic makeup under the new plan. According to the estimates, white attendance would rise and black attendance would fall at nearly half of Wake County elementary schools.

“I am concerned with what I see as the trends in socioeconomic and racial balance,” board member Christine Kushner said during a break. “We need to keep looking at that.”

Massachusetts education consultant Michael Alves, who was brought in by business leaders to develop the forerunner of Wake’s choice plan, defended the plan Tuesday. Alves, who is being paid by Wake for use of his assignment software, said the new plan has accomplished the goal of providing stability. He said critics have forgotten the distress that student reassignment brought families under the prior plan.

“The implementation of this plan has gone very well,” said Alves, who attended a school board work session Tuesday afternoon. “There’s a difference between families not getting what they want and the management and implementation of the plan.”

One of the largest changes was projected at Lead Mine Elementary in North Raleigh, where white attendance is projected to increase by 7 percentage points and black attendance to decrease by 3.7 percentage points. Under the former address-based system, Lead Mine drew students from an area near Capital Boulevard, about 6 miles south and east of the school, as well as from neighborhoods immediately around Lead Mine Elementary.

Under the new system, no address is tied to a specific school.

“You have set up an assignment plan that says to our community, ‘Let’s only teach the ones that matter,’ ” former school board member Beverley Clark said.

Perhaps because of what Tata has called widespread approval of the system, no speakers voiced support of the new assignment plan. Several of those who spoke in opposition were active in support of the Democratic-majority board that was elected last fall. Speaker Rita Rakestraw unsuccessfully ran against current Republican board member Chris Malone in 2009.

“Nothing in this choice plan prevents the creation of high-poverty schools,” Rakestraw said. “Now it’s heartbreaking to see our schools turn into ‘have’ and ‘have not’ schools.”

Board member John Tedesco said demographic shifts were more severe under the old plan. He said that Wake parents generally like the new plan, but also pointed out that it’s a long-term plan just getting under way.

“Most parents think it serves the schools and the community well,” Tedesco said.

Goldsmith: 919-829-8929