He was 73.
Dr. Wheeler had presided over the board's Monday evening meeting.
"I am deeply saddened by the news of the unfortunate passing of Dr. Leonard D. Wheeler," said Harford County Executive David R. Craig in a statement released Thursday.
"Dr. Wheeler had a distinguished career as an educator and served with distinction and integrity as a member of the Board of Education," said Mr. Craig. "He worked tirelessly to help make Harford County Public Schools one of the finest school systems in our state."
"Serving as school board president is possibly the most challenging civic responsibility anyone can engage in. He was a kind, gentle and quiet leader who was extraordinarily knowledgeable about education, curriculum and the day-to-day operations of our school system," said Robert B. Thomas, a former Harford County school board president who is now a county government spokesman.
The son of a shoemaker and a homemaker, Leonard D. Wheeler was born in Washington and spent his early years there, and later moved to Baltimore.
He was a 1956 graduate of Frederick Douglass High School and earned a bachelor's degree in 1960 from what is now Coppin State University. He subsequently earned a master's degree in 1967 from Morgan State University and a doctorate in education in 1984 from Temple University in Philadelphia.
From 1961 to 1969, Dr. Wheeler was a classroom teacher, and in the early 1970s was an assistant principal until being named principal of Harford Heights Elementary School.
He was assistant superintendent for federal and state programs from 1979 to 1984, and from 1989 until retiring in 1992, Dr. Wheeler was assistant superintendent of elementary education.
In addition to his work with city schools, Dr. Wheeler had taught at Morgan State from 1987 to 1984 and had been an associate professor in the education department at what is now Notre Dame of Maryland University.
Dr. Wheeler had been active in Democratic politics in Harford County and had run unsuccessfully in 2006 for a County Council seat.
At the time of his 2008 appointment by Gov. Martin O'Malley to the Harford County Board of Education, Dr. Wheeler had been a member of the Judicial Nominating Commission and the Harford County Board of Elections.
"He was an absolute pleasure to work with, and we spent lots of time together. We'd met every Wednesday for an hour and sometimes it was two or three hours," said Francis F. "Rick" Grambo, who is vice president of the board. "He cared about the school system and gave us his best and came at a time of great transition for the board."
Mr. Grambo, who is an electrical engineer and vice president of Pritchard Brown in Baltimore, said Dr. Wheeler went to great lengths in listening to all board members' opinions.
"He wanted everyone's voice to be heard and as a result, we operated as a cohesive board. He was always teaching us and helped me grow. He was my mentor," said Mr. Grambo.
"He was also an inspirational man. If he got a letter, he would answer it in a heartfelt manner and inspirational words," he said. "And he closed every meeting with the same words: 'Give my best to your families.' He will be sorely missed."
"I think his greatest frustration on the board was dealing with the political aspect of education. He did an outstanding job during very challenging times when money was very tight when it came to operating and capital budgets," said Mr. Thomas.
Dr. Wheeler was an active member of the National Association for the Advancement of Colored People and was a past trustee of the Woodbourne School, New Hope Academy, Harford County Partnerships for Families and the county's CORE Services Agency.
Dr. Wheeler was also a longtime active member of Ames United Methodist Church, where he was a lay minister.
His hobbies included listening to classical music and jazz, writing, reading and following politics.
Funeral services will be at 10 a.m. Tuesday at his church, 112 Baltimore Pike, Bel Air.
Surviving are his wife of 27 years, Dr. A. Barbara Wheeler, superintendent of Kent County public schools, who lives in Bel Air and Chestertown; two sons, Christopher D. Wheeler of Bel Air and Leonard B. Wheeler of Baltimore; two daughters, Evangeline Wheeler and Vell Wheeler, both of Baltimore; two brothers, John Wheeler and Warren Wheeler, both of Baltimore; three sisters, Clarene Wheeler, Debrah Wheeler and Jackie Anderson, all of Baltimore; and three grandchildren.