Blackburn, elected in 1998 to the first of her three terms, made her announcement this morning during the Board of Education meeting.
"After a great deal of soul-searching and thoughtful introspection, I want to announce that I will not be seeking re-election to the school board this November," Blackburn said, reading from a prepared statement.
"While I know this may come as a surprise, I feel that it is time for me to step back and allow another concerned, dedicated citizen to fill this most honorable role in our community," she said.
Blackburn, a retired middle school history teacher, represents the county's District 2 that covers much of the Martinez area.
She recently was elected by her fellow board members to serve as vice chairman of the board for 2010.