Special Needs and Walt Disney World, help?!?

I live in Florida, so I have been to Disney multiple times. This time is, however, different; I will be taking my Down-Syndrome friend to Disney for 4 Days in a few months. He has Mosaic Down-Syndrome, so he is very functioning (speaks 2 languages fluently). Has anyone taken any special needs kids to Disney? Is anything different? What should I expect? I noticed the last time that I was there that special needs kids were being let into a separate entrance. He doesn't have any disabilities (other than being quite overweight), but it would be a great help as he can be very impatient. How does this work? Thanks.