This past summer, from evangelical churches nationwide, more than one million of the faithful departed for the mission field, taking up Jesus’ “Great Commission” to “go and make disciples of all nations.” The churchgoers hoped to convert souls, establish churches and meet other human needs. But they did not intend to serve for years or whole lifetimes, like such pioneers as Jim Elliott, who was killed in Ecuador in 1956 evangelizing to native people; or Hudson Taylor, the founder of the China Inland Mission; or even the awful fictional caricatures of African missionaries in Barbara Kingsolver’s novel The Poisonwood Bible. These new missionaries came home after only a week or two.

Short-term mission trips to Africa, South America and Southeast Asia have become very popular in the past few years. They are a keystone strategy of evangelical pastor Rick Warren’s plans to help Rwanda. These trips, like Christian missionary endeavors overall, encompass a wide variety of activities, from evangelization and “church planting” to health care and economic development. The billion-dollar question, however, is whether they’re worth the cost. Are short-term missions the best way to achieve the goals of Christians? Critics argue that sightseeing often takes up too much of the itinerary, leading some to call short-termers “vacationaries.”

It’s hard to judge the fairness of this characterization, since almost no one runs the numbers. Estimates of how much churches spend on short-term missions go as high as $4 billion a year, according to the Capital Research Center. The literature is sparse, most of it focusing on the spiritual aspects, for the missionaries themselves. And these aspects are sometimes oversold.

Calvin College sociologist Kurt Ver Beek surveyed U.S. missionaries who built homes in Honduras after Hurricane Mitch in 1998. After coming down from a post-trip “high,” the short-termers did not evince much change in their lives. Only 16% reported “significant positive impact,” including in prayer, friendships and financial giving. Then Mr. Ver Beek surveyed those whose homes were rebuilt by missionaries and those whose homes were rebuilt by local nongovernmental organizations. He found that there was “little or no difference” in the spiritual response of the beneficiaries.

The economic impact of the Honduras trips seems in line with similar missionary stints: Teams spent $30,000 to build a home, according to Mr. Ver Beek, that would have cost $2,000 to build with local labor. With these kinds of spiritual and economic results, the effectiveness of short-termers in the work of Christian missions is questionable.

Indeed, if you were to ask an economist about short-term missions, many of which involve such manual-labor projects, he would have a simple answer: Ditch the traveling team members and send a check. A career missionary knows better what manual labor needs to be done on-site, and he can hire local laborers for much less money than what flying in unskilled Americans requires. Using local labor contributes to the local economy and avoids perpetuating a culture of dependency and powerlessness. A career missionary is also fluent in the local language and culturally aware, so he can be more effective at evangelism, discipleship and social-justice ministries.

Today, many churches and mission programs are giving up any sort of economic justification for sending American teenagers to construct cinder-block buildings and treat people for head lice. Instead, they are billing the trips as “cultural exchange,” “service learning” or “solidarity” ventures. This sort of rationale gets more at what the missionary philosopher Lesslie Newbigin referred to as the Christian mission of “learning”: “When he sends them out on their mission, Jesus tells the disciples that there is much for them yet to learn, and he promises that the Spirit who will convict the world will also lead them into the truth in all its fullness.”

Even so, the short-term mission paradigm is of somewhat limited use in meeting the goals of Christian mission. The faithful can do better. First, churches might want to encourage more one- and two-year commitments and fewer one- and two-week jaunts. The Southern Baptist Convention’s International Mission Board, for example, has only about 1,200 missionaries in its one- to two-year programs, compared with the 30,000 short-termers it sends out every year. Of the IMB’s 4,200 career missionaries, more than 40% were once sent through a one- to two-year program.

Christians in North America might also want to focus more of their resources on cultivating human capital in the mission field. Who better to meet the needs of, say, Rwandans than a Rwandan? Furthermore, it is often no longer necessary to send missionaries to evangelize the developing world. In Africa and South America, evangelical churches are growing by leaps and bounds, with Christians on each continent vastly outnumbering their brethren in North America. Anglican archbishops in Africa have even set up “missionary dioceses” in the U.S. and Canada.

Americans should therefore look to their comparative advantages, one of which is education. The U.S. has hundreds of accredited evangelical seminaries and Bible colleges — not to mention thousands of universities that offer religious education — far more than are available in the Global South. And our seminaries are some of the best in the world, combining first-class biblical scholarship with evangelistic passion. We should be bringing more pastors and church leaders to the U.S. to study — or, even better, figuring out ways to reproduce our religious- education system in the places where it is most needed. All of which should help Christians pursue the “Great Commission” more effectively.

This article was originally published in the Wall Street Journal on October 10, 2008.