American teachers have not always been afforded the luxury of teaching evolution forthrightly. John Thomas Scopes, for example, was famously prosecuted for violating Tennessee’s ban on teaching evolution in 1925. Although his conviction was subsequently overturned, a national survey of high school biology teachers conducted in 1939–1940 revealed that only about half were teaching evolution as a central principle of biology.
Between 2007 and 2019, there definitely was progress: from 51 percent of high school biology teachers reporting emphasizing evolution and not creationism in 2007 to 67 percent in 2019. It was matched by a drop from 23 to 12 percent of teachers who offer mixed messages by endorsing both evolution and creationism as a valid scientific alternative to evolution, from 18 to 15 percent of teachers who endorse neither evolution nor creationism, and from 8.6 to 5.6 percent of teachers who endorse creationism while not endorsing evolution.
What accounts for the improvement?
The results of the 2019 survey suggest that a concerted effort to improve state science standards helped to improve evolution education. The Next Generation Science Standards (NGSS), which debuted in 2013, include “Biological Evolution: Unity and Diversity” as a disciplinary core idea of the life sciences at the middle and high school levels. By now, 20 states (plus the District of Columbia) have adopted the NGSS, and a further 24 states have adopted standards based on the same evolution-friendly framework on which the NGSS are based.