I grew up and went to public school in rural Tennessee. Evolution, while technically part of the curriculum, was not taught, for two reasons. Either the teacher was religious and did not believe in it, or the teacher was scared of angry parents/administrators. In two years of biology courses, the word evolution was not mentioned once (creationism was not mentioned either, the whole topic was just ignored). While it would be nice if this law gave the latter group the confidence to teach the curriculum, I don't expect that to happen. In most rural schools nobody wants to shake things up too much; that is, while a teacher may have legal protection, the massive headache that vocal parents and community members would cause for him or her would not be worth whatever satisfaction was gained from teaching the facts.

I'm honestly not sure what educational gains can be made from legislation in these environments. If evolution is forced into the curriculum, religious parents will tell their children to just put the answers that the teacher wants on the test but that what they're learning is part of some liberal/satanic/whatever conspiracy. Others will homeschool. Ultimately, curious children or children with parents who understand both evolution and the educational system will end up with the critical thinking skills necessary to sort out truth from fiction. Those skills are more important that teaching people to memorize facts about evolution anyway.