On Monday, 12,000 Upper Darby students will head back to class in a district still embroiled in its summer-break drama - one that publicly opened with the surprise ouster of its superintendent and flared into a dispute over alleged racial imbalances that has drawn the attention of the NAACP.

The root of the ruckus, however, goes further back to the past school year, Superintendent Richard F. Dunlap Jr.'s third - and last - at the helm of one of the most diverse districts in the region.

Dunlap had floated a plan that would have relieved class overcrowding at certain elementary schools by assigning children to schools outside their neighborhoods. But after a closed school board meeting July 20, he abruptly left his $194,866-a-year post. Some in the community contended that his proposal, and its potential to change the racial makeup of some mostly white schools in the township, was his undoing.

Now, a Delaware County NAACP chapter is saying it will investigate whether the Upper Darby School District discriminates by keeping lower-income minority students in overfilled schools, as well as by busing nearly 300 from the Millbourne section to a rented building six miles away in Glenolden, outside the district.

Covering an urbanized area on Philadelphia's western border, the district is 47 percent African American, 32 percent white, 14 percent Asian and Pacific Islander, and 6 percent Hispanic or other ethnicities, according to state data. Those groups are far from evenly distributed through the school system. At five of the 10 elementary schools, the student populations are 85 to 96 percent minority.

The NAACP is "concerned about anyone who opposes the best education for all kids, who supports segregating children, so . . . we are doing some investigating," said Joan Duvall-Flynn, president of the Media branch and a member of the group's state conference.

She said the NAACP turned its attention to Upper Darby after she got a call from a community member. She said she had yet to inform the district.

In addition to asking the U.S. secretary of education to look for civil rights violations, Duvall-Flynn said her chapter wants to interview district employees and board members, and might hold public hearings so residents can discuss the situation.

"It is something that fits under equitable services to all children," she said.

Calls seeking comment from school board president Judith Gentile, district solicitor Frank Catania, and Dunlap were not returned.

Allegations of racial bias are not the only unresolved issue in Pennsylvania's eighth-largest district. The school board is conducting a search for Dunlap's replacement; in the interim, Assistant Superintendent Dan Nerelli is leading the district.

Board members have offered shifting accounts of the departure of Dunlap, who last fall signed a new five-year contract. At a meeting last week, board president Gentile announced that Dunlap had retired following a vacation. On July 21, she had said he was on a paid leave of absence.

Sources familiar with the board's actions said Dunlap was fired after the board met July 20 with a select group of administrators who were critical of him and his plan to even out enrollments at the elementary schools, where class sizes range from about 18 to 29.

Dunlap had proposed flexible attendance boundaries for the district's elementary schools. He then could have redistributed students by taking a portion of those in overflowing buildings and sending them to other schools, including those in the more affluent Drexel Hill area - Aronimink, Hillcrest, and Garrettford. Those three, plus Primos and Westbrook Park, are more than 50 percent white.

District records, available online, show that all of the elementary schools have some classes or grades that exceed the target size.

Dunlap also wanted to introduce full-day kindergarten and build a new school in the lower-income Bywood section, saving millions of dollars by eliminating busing and rental of extra space. The Glenolden building housing Walter M. Senkow Elementary belongs to the Archdiocese of Philadelphia.

During his tenure, he also hired more minority teachers and principals, and instituted diversity training for the overwhelmingly white staff.

Dunlap's redistricting plan was denounced by a broad swath of the community, from parents, teachers, and administrators to local politicians.

Critics included Upper Darby Mayor Thomas N. Micozzie and State Rep. Jamie Santora (R., Delaware), both of whom said the new attendance boundaries would hurt real estate sales, since buyers wouldn't know which school their children would be attending. Micozzie has said he thought Dunlap "did a poor job" as superintendent.

Another Upper Darby state representative, Margo Davidson (D., Delaware), maintained that racism was behind many of the complaints about Dunlap. She said some people don't want students "from the other side of Lansdowne Avenue" attending Drexel Hill schools.

Micozzie and Santora denied their objections were racially motivated.

Many in the district have close ties to the Republican-controlled township government. Micozzie's daughter, Nina Tyre, is a supervisor of benefits and compliance and president of the Upper Darby Association of School Administrators; Greg Manfre, director of students affairs, is the brother of Upper Darby Councilman Marc Manfre; Edward Monaghan, the district's coordinator of attendance, is a councilman.

Some of those administrators were among the 24 invited to the July 20 school board meeting to discuss Dunlap's performance, said sources familiar with the meeting.

One of those not present, director of operations Matthew McKenzie, wrote a scathing letter to the board criticizing the "procedural unfairness" of the meeting, to which only those who did not support Dunlap were invited. McKenzie sent the letter by email last week.

He also chastised the board for "making a substantially expensive and irreversible mistake" in removing Dunlap.

"The very premise of Dr. Dunlap being anything other than an exceptional leader is entirely inaccurate," McKenzie said. None of the four administrators who report directly to Dunlap were asked to attend the meeting, which McKenzie called a "charade."

Dunlap, McKenzie said, "was working on the best way to create equity throughout the district . . . all while sustainably saving millions of dollars annually."