I like your choice of the word “publicist” instead of “public relations officer”, which sounds sort of dishonest (like a sleazy politician justifying some dirty deals). I would disagree with you, however, when it comes to when to explain things. Your post seems to say that you wait until parents voice an objection before explaining your choice of strategy (perhaps I misread your implication).
Some parents may not be willing to directly confront the authority figures represented by teachers. Instead, they will sabotage your efforts by badmouthing you in front of their children or other parents. They may even pull their children out of school (assuming they have such a choice) without openly voicing objections.
Thus, if there is a need and a will to engage in publicity, it should be proactive. Parents need to be gently persuaded that ongoing innovations are being done for the sake of improving outcomes, and that teachers really do have their children's best interests at heart.