I think there are two parts to the response Macron should have made.
Firstly condemn outright the use of violence as a political and religious weapon (and I assume we are all in agreement here, and that in fact Macron probably did make some statement to this effect).
[Additionally given the case in point compare the violence to some of the recent atrocious acts of the US against muslims. This would certainly make some in the muslim world sit up and think
and also take some of the wind out of the sails of (potential) terrorists. Realistically this is never going to happen. I mention it because the connection is of the utmost importace, the current violence more or less directly stemming from the war on terror.]
Secondly, announce a governmental inquiry/review into the use of materials that can be considered blasphemous in the public school system. Or better words to that effect, clear enough that it should cover the teachers actions and any similar sorts of cases in the past, present or future. This shows that the government is concerned about what happened but also allows for a reasoned detailed examination of the problem of conflicting values which goes deeper than a right/wrong binary. And allows for the conclusions/proposals to become public at a time when the hotheads on both sides have cooled off somewhat.
But then thinking of myself as Macron I am undoubtedly failing to take the opportunity to whip up more religious hatred and further my chances of re-election.