Isan is the poorest area of Thailand. This is due to bad climatic conditions (often hot and not enough rain). The south part of "ISAN" area (Buriram, Surin, Si saket, Ubon Ratchatani) and also the area around Khon Kaen are really poor areas. Those areas are really dry with less rain than in other Isan area.
In year 2000 there were 20.8M inhabitants in Isan. 68% of the people have completed less than 7 years of formal education. 1998 GDP per capita was 35% of the national average so making Isan a poor area to live.