Are donations to charter public schools tax deductible?

You are correct. In order to be a deduction, the donation must be made to a 501(c)(3). BEWARE, Just because the feds have granted that status does NOT mean that the organization is recognized as a charitable organization in your State. In order to get a deduction that will be allowable on both your federal and state income tax returns, check the State status with your Secretary of State's office.