WASHINGTON — The number of Americans who volunteer to mentor students, beautify neighborhoods, and pitch in after disasters is at a 30-year high, fueled in part by a boom in teenage participation, a new study says.

The report by the Corporation for National and Community Service tracked volunteer rates since 1974. It found that more than 1 in 4 adults — or 27% — currently give time to their communities, a jump from a low of 20.4% recorded in 1989.

Teenagers between 16 and 19 saw the biggest jump, with 28.4% volunteering compared to just 13.4% in 1989.

Service among midlife adults (ages 45 to 64) and senior citizens (ages 65 and over) also remained strong at 30% and 23.5%, respectively. The study, which is set to be released today, credits higher education levels, delayed childbearing and longer life expectancy.

“We are encouraged that emerging studies consistently show increased volunteering by young Americans. If supported properly, we may be on the cusp of a new civic generation,” the director of research and policy development at the corporation, Robert Grimm, said.

The group, which promotes volunteering through federal programs such as Senior Corps, AmeriCorps, and Learn and Serve America, attributed increased volunteering among youths to a rise in service-learning programs in schools and colleges that combine classroom study with community work.