The Machiguenga traditionally live in small semipermanent settlement clusters of 7 to 25 individuals, composed of one to four families, situated on hilltops and ridges for fear of slave raids. In the past, charismatic leaders or shamans attracted several hundred people along a tributary stream. Since the 1960s, Matsigenka schoolteachers, trained in Pucallpa by the Summer Institute of Linguistics (a Protestant group), have successfully drawn people out of their isolation into school communities with airstrips. But most Matsigenka households continue to be scattered in traditional hamlets to avoid competition over resources. Individual families periodically leave on foraging trips for several days or weeks at a time. Matsigenka school communities range in size from 100 to 250 individuals and consist of nuclear and extended family households averaging approximately 6 individuals per household. Houses are constructed entirely from local materials; they are built with heavy hardwood posts tied with bark, palm-wood walls, and a thatched palm-leaf roof. Houses were traditionally low, oval-shaped structures; today many have raised palm-wood floors and are larger and rectangular in shape. Houses are located at the edge of a river or a stream and are usually surrounded by a clearing with a small kitchen garden at the perimeter.