Part of the weight change between program-start and program-end depends upon how physically active your role is, and whether it's indoors or outdoors. Photographers typically lose more weight than vacation planners, for instance.
If you're underweight or on the low-end of normal weight: it's somewhat common to gain weight as your body builds muscle mass from the added exercise and physical exertion. Excessive eating out or eating junk occasionally causes fat gain for some CPs, which is why cooking your own, healthy, food makes all the difference in the world. Yeah, CPs don't get paid a lot, but compared to the cost of eating out the cost of groceries is actually relatively cheap.
If you're already overweight: unless you have an extremely sedentary role or consume 3,500 calories per day - you'll lose weight. How much depends on your initial starting weight (heavier people burn calories faster), the length of your program, and your role.
I was a photographer and lasted for four and a half months. When I started I was a whopping 355 pounds, but I left at 310. Average weight loss of just a hair under 3lb/week, the highest "safe" range of weight loss. Lost count of the number of times I had to go to costuming for smaller sizes!
Of course, having a very active job when you weigh 300+ ultimately led to health problems, which ultimately led to a very ugly record card. Down to around 295 now (weight loss slowed post-Disney, but didn't stop) and would like to go back at some point.
Oh, and a friend of mine worked Fall Advantage. Lost 105 pounds between the end of May and the beginning of January.