For my daughter's school district, a 504 was a way of appeasing parents. You get the same type of meeting and write-up as for an IEP but it does not have to be followed. If you're lucky, you'll get a teacher who will try hard to follow a 504 but if it can't be followed, oh, well, too bad. An IEP has to be legally followed. (If you can't tell, I'm rather cynical when it comes to a 504. Since they don't have to follow the "suggestions," it is worth about what the value of the paper it is written on, if that.) However, most schools will require that a 504 be tried before they'll even consider an IEP.