Proposition 18, which would have allowed 17-year-olds to vote in primary and special elections if they turn 18 before the next general election, was rejected by California voters.

The proposed amendment to the state Constitution would have permitted California to join at least 18 other states that allow some 17-year-olds to cast ballots, including red states such as Kentucky and Mississippi and blue states such as Illinois and Maryland.

The ballot measure was endorsed by the California Democratic Party, along with party leaders Gov. Gavin Newsom and Secretary of State Alex Padilla. Supporters argued that the measure would have helped encourage young Californians to engage in the political process, and provide a real-world understanding of what they learned in high school civics classes.

The California Republican Party opposed Proposition 18, along with the anti-tax Howard Jarvis Taxpayers Assn. Opponents argued that 17-year-olds should not be able to vote on complex tax and bond proposals that will not directly affect them, and they also questioned whether most high school students that age have enough maturity and life experience to take part in an election.

The Democratic-controlled Legislature voted in June to place Proposition 18 on the ballot.

Assemblyman Kevin Mullin (D-South San Francisco), one of the authors of the proposed constitutional amendment, said Proposition 18 was a modest effort to expand voting rights in California because the 17-year-olds eligible to vote were close to 18 anyway. Mullin’s father, former South San Francisco Assemblyman Gene Mullin, first introduced the measure 16 years ago.