If I understand you correctly you are looking for three things:
1. Disciplinary action against Dave P.
2. Correction of the scientific errors made by Dave P.
3. An apology from Dave P.
For #1, the BOE has stated that they have taken action against Dave P. However, by law, based on the union's contract, they are not allowed to publicly discuss the type of or severity of disciplinary action unless the teacher grants them permission.
Is your threat of a lawsuit because you do not believe them? Or just to discover through the court proceding what the action was?
For #2, as previously stated, the district does provide a cirriculum teaching the science that you agree with. Dave P. is not qualified to make the corrections that you are requesting, so other than the current science cirriculum, what more do you want?
For #3, a personnel apology from Dave P. is not within the control of the BOE. They cannot force him to do that. What do you want a lawsuit against the BOE to accomplish in this regard?