When it comes to the matter of schools and evolution, the primary motive for teaching evolution in schools is to attract students to atheism and/or a naturalistic worldview at a early age and in a way that is not easily challenged by many parents. In other words, teaching evolution puts youngsters on a path towards atheism. The better the student, the more positive the reinforcement, and the more likely this approach will attain its desired effect.
If schoolchildren were permitted to believe (and say) that evolution is less likely than intelligent design, it would contradict the philosophical underpinnings of unguided evolution. This would lead students to question, even to reject, such materialist philosophies as atheism and secular humanism.
A more honest way of teaching about evolution would not be to present it as an unquestionable dogma, but simply to tell pupils what it is, how many scientists of various types believe in it; then to present all the scientific evidence for and against it.
For students who are mature enough to understand the philosophical implications, say, beginning with the upper three grades of high school, educators could explain the ideological links between evolution and various philosophical and political schools of thought: materialism, atheism, eugenics, Nietzsche, etc.
Similar links could be explored for ideas which criticize evolution, such as intelligent design which accepts some aspects of evolution while denying the lack of guidance, and creationism, which begins with the premise that God created everything.