Jonathan Nguyen conducts his summer science class inside a library, but his students don’t whisper as they twist together DNA models or join an assembly line of peanut butter sandwich-making to learn more about genetic mutations.

Many students say it’s a change from their school-science classes, said Nguyen, a biology and anatomy teacher at Pennsauken High School in Pennsauken, New Jersey. The students “are so gun-shy about things like ‘don’t make a mess’ and ‘don’t make a mistake,’ ” he said, “and in science you’ve got to do both.”