I personally don't think the theory of evolution should be taught at all in high school. And to make this post on-topic, here are the reasons.
Evolutionary theory as well as the evidence that support it are very complex and take a life time to learn and fully appreciate. More often than not, there isn't anywhere near enough time in a high school biology semester to adequately teach the students (a) the appropriate disciplined methodology to approach a scientific endeavor, (b) the skills to objectively and logically interpret the evidence and data, (c) the creativity required to connect all the evidence (or at least enough evidence) for a scientific theory, and (d) humility.
What happens is that more often than not the evidence for evolution are presented for students to swallow and regurgitate later on. In many cases, this would result in some students achieving a high grade on the subject without really understanding the how's and the why's about the evidence. Furthermore, it would result in high school graduates who think they know enough about evolutionary theory to speak authoritively on advance matters.
My belief on the matter is we should emphasize much more on the discipline of science than the actual theories themselves. Once the students adequately understand how to approach a problem in the correct scientific manner and have learnt enough to know that they know very little about the real world, THEN they can be taught the theory and the evidence and data.
In other words, I think that we are doing more harm than good by shoving evolution down high school students' throats.
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