He becomes the second African-American state schools superintendent in California history.
Seven out of 11 board members will remain on the board after Jerry Brown leaves office.
Outcome of race a major victory for California Teachers Association and allies, and a major defeat for leading charter school advocates.
Thurmond erases 86,000 vote lead by Tuck on Election Day and now has a 75,000 vote lead based on partial count of millions of mail-in and other uncounted ballots.
As of Thursday evening, election results show Marshall Tuck leading Tony Thurmond 50.6 percent to 49.4 percent, a margin of about 69,000 votes.
An EdSource estimate finds that the governor-elect's education promises could add up to billions of dollars.
High-spending campaign for a job with little power but a big megaphone comes down to wire.
Contest between Wilson Riles and Max Rafferty in 1970 far more incendiary than current race for state superintendent of public instruction
California's new governor will be the key player in introducing new reforms. But where the funds to pay for them would come from is anyone's guess.
Whether it's clamping down on charter schools or changing teacher tenure, candidates can say a lot more than they can actually do.
EdVoice and the California Teachers Association are making their influence felt in dozens of campaigns for Assembly and Senate.
Poll shows Marshall Tuck favored by two-thirds of Republicans, half of independent voters, and one-third of Democrats in the week before the Nov. 6 election.
Marshall Tuck has a more 2-to-1 advantage over Tony Thurmond in direct donations and $28.7 million in funding from independent committees.
Organizers are attempting to reverse the historically low turnout among young voters.
Negative ads tie Marshall Tuck to the Trump administration and blame Tony Thurmond for problems in a district where he was a board member.