Schools should be arms of the communities in which they exist. Part in parcel of those communities include the parents of the children in those schools, and those parents undoubtedly influence the communities values and morals. In this way, those parents should be permitted to influence some of the things taught in school.
There are many factors to take into account when considering education, for instance, demographics, culture, religion and economic status. There are children who attend Christian schools and Catholic schools which is an indication that the parents of the students who attend those schools want Christianity and/or Catholicism to be part of their children’s education. Likewise, if capable, some parents send their children to private schools as they believe there are certain aspects of education that are present in that forum verses a public school.
I believe that parents should have at least some say in what is taught in schools. This is especially true when it comes to some of the more controversial subjects, like sex education. It is not the government's right to decide what and when our children should learn about certain subjects, it is the parents job because they are personally responsible for them.
Schools are meant to give students a well-rounded education in all manner of subjects. This involves experts in all those subjects. Last I checked, parents are not experts in all subjects. I can't tell you how many times I've been scolded by parents for trying to teach a basic biological fact. They were not being mean, they just didn't know the actual facts. Schools should teach facts, not morals or values, but facts. Parents should not have a say in what facts are taught. They should have a say in what they teach their own children about morals.
I was set to voice a "yes" opinion to the fact that parents should have a say in what their children learn at school - and they really should. However, upon noticing that no one ever disagreed, I considered that fact that teachers and curriculum designers have five or more years of schooling each, are generally required to be in agreement about what the students are taught, and must get their opinions past at least a hundred or so people per town. That this many good opinions could go drastically wrong is an unlikely scenario. Parents frequently know far less than just a single schoolteacher's knowledge, and especially about what teaching materials and methods are best for their child. Maybe as Americans we still poke our noses into too many unnecessary places.