What an appropriate question. I am assuming you are teaching biology, is that right? As in all things, collaboration is the key. If your teaching colleagues (K-12) agree and support the scientific method, then you will present a unified front on this topic. The more exposure and experience your students have in related science classes over the YEARS, the better prior knowledge base about evolution they will have in high school.
The power of personality is also important. If your students think you are interested in them and your subject, they often will give what you teach a fair hearing.
Having said that, I will tell you that there are some places where it is considered a mortal sin to even listen to anything related to evolution or a long time frame in the history of the universe.
Let me give you an example.
I was teaching Chemistry and we were discussing atomic decay. I was using the example of using atomic decay to measure time for the entire globe and set atomic clocks. Well, one of my students shouted out, "We don't believe in evolution!"
See, these kids learn, over the YEARS, not to accept anything that supports time measurement...including things like the Red Shift. This is anathema to their cultural and religious world view.
For more info: Evolution Outreach Projects