no caste system in Thailand-- there is lots of upward mobility here.
yes the Bangkok Thai-Chinese look down on the rural poor, but lets be honest, people from certain parts of the U.S. are also looked down on.
I have lived in the same area of Thailand as Annie (N.E. Thailand) for many years; first as a volunteer teacher at a very poor school and then as a business owner. the change in the area since I first arrived is incredible. when I arrived in the early 90s there were no cars in the villages and farmers were still using water buffaloes, now, the water buffalo has been replaced by tractors and cars are common place. I even spotted a pick-up parked outside Annie's house.
my wife is one of 10 children from a typical farming family (no running water or inside bathroom when she was young). she and a brother and a sister became teachers. the brother is now a school director and his daughter is a medical doctor. one of her sisters who remained a farmer has 4 children, all college educated and working in corporate jobs. another brother has 2 sons and 2 daughters. the daughters went of to college and now work in Bangkok in IT jobs. the sons were lazy and now work in crummy jobs for minimum wage. all the kids that went to college received government student loans and attended college in N.E. Thailand. many of the students I taught have also gone off to join the middle-class with good jobs.
there is a popular phrase in Thailand called "mai pen rai" which roughly means "don't worry about it" and many attribute this to the care free attitude many Thais have to life. but it is this attitude that actually keeps many Thais down. for example: if a child does not do his homework, the parent might say "mai pen rai, he is just a kid". well, this is why the 2 sons in the paragraph above are now working for peanuts. long story short: getting out of poverty here is not impossible or even that hard, probably much easier than in the US., it just takes some effort and the right attitude.