Worried that public schools are failing to prepare students for a complex and changing world, educators unveiled new guidelines Tuesday that call for sweeping changes in the way science is taught in the United States, emphasizing hands-on learning and critical scrutiny of scientific evidence.

Among many other changes, the guidelines call for introducing climate science into the curriculum starting in middle school, and teaching high school students in detail about the effects of human activity on climate.

The guidelines also take a firm stand that children must learn about evolution, the central organizing idea in the biological sciences for more than a century, but one that has rallied state lawmakers and some religious conservatives to insist that alternative notions like intelligent design be taught.

Though they could become a focus of political controversy, the climate and evolution standards are just two aspects of a set of guidelines containing hundreds of new ideas.

The guidelines, known as the Next Generation Science Standards, are the first broad national recommendations for science instruction since 1996. They were developed by a consortium of 26 state governments and several groups representing scientists and teachers.

States are not required to adopt them, but 26 states have committed to seriously considering the guidelines. They include Arizona, Arkansas, California, Iowa, Kansas and New York. Other states could also adopt the standards.

Educators involved in drawing them up said the guidelines were intended to combat widespread scientific ignorance, to standardize teaching among states, and to raise the number of high school graduates who choose scientific and technical majors in college, a critical issue for the country’s economic future.