Despite their reputation as symbols of baby-boomer America, Protestant megachurches attract a younger crowd and more singles than the average Protestant church, according to large-scale study released Tuesday.

The survey also found distressing news for a movement that took off in the 1980s and remains influential in evangelical Christianity: megachurch-goers volunteer less and give less money than other churchgoers.

Conducted by the Hartford Institute for Religion Research at Hartford Seminary and Leadership Network, the survey of nearly 25,000 people who attend 12 U.S. megachurches was conducted from January through August 2008. It is billed as the largest representative national study of that religious demographic to date.

An estimated 5 million Americans a week attend roughly 1,300 U.S. megachurches, defined in the study as Protestant churches with attendance of 2,000 or more.

To compare the megachurch data with Protestant churches of all sizes, the study relied on the U.S. Congregational Life Study of 2001.

Among the megachurch report’s highlights:

• The average age of megachurch attendees is 40, compared with nearly 53 at a typical Protestant church. Nearly two-thirds of megachurch attendees are under 45, double the numbers in Protestant congregations of all sizes. The vast majority are between 18 and 44.

• Nearly a third of megachurch attendees are single, compared with 10 percent in a typical Protestant church. They also tend to be wealthier and better educated.

• Nearly all those surveyed — 98 percent, including visitors — described themselves as a “committed follower of Jesus Christ.” Nearly a quarter hadn’t been in any church for a long time before coming to the megachurch.

• Sixty-two percent of megachurch attendees said they had experienced much spiritual growth in the past year. But that does not always translate to behavior churches expect of members: nearly 45 percent of megachurch attendees never volunteer at the church and 32 percent give little or no money to the congregation.

“The ethos of the megachurch is to say ‘You can’t just sit there and spectate, that’s not enough, you’ve got to do this or do that,'” said study co-director Scott Thumma, a sociologist at the Hartford Institute for Religion Research. “But a lot of people said ‘I’m perfectly happy coming here and doing that.'”

Divided loyalties also might play a role: just three-quarters described the megachurch they were attending as their “home” church, and many said they were attending more than one church.

Thumma said the findings don’t necessarily mean that megachurches fail to foster involvement. The study found that significant numbers of even the least involved participants still give generously, have invited others to church and attend services weekly.