"I recently made an impulsive and unprofessional response on my personal Twitter account regarding Kamala Harris," wrote William Formica in the apology letter on August 23.
He was accused of writing that Harris performed a sex act in response to a question about the vice president's political accomplishments.
He apologized to the board last week, saying that the incident had become "distracting."
Formica then clarified that the remark was directed at a national political figure and not anyone in the community.
The apology comes weeks after outraged parents at a Souderton Area School Board meeting demanded Formica's resignation.
"I am not someone who avoids discussions or hides behind a computer screen. Therefore, I will be reiterating this apology at the upcoming Board meeting on August 29th," said Formica.