Children that are 1 SD below avg. need differentiation and I believe they need it on both ends. Children in the 115-140 could definitely benefit from differentiation. I was just talking with my friend the other day about her daughter. Her daughter is 5 and will be starting K in the fall. She was recently tested with a 130 IQ (had to get tested for speech) and she is doing some double digit addition already. She can read some words already, and will probably be reading more before school starts. She is incredible artistically as well. My DS5 who is PG was doing advanced math when he was her age (probably 5th grade at least) and reading at a 6th grade level at least as well as many other things. So clearly my DS needed differentiation. But that doesn't mean that this other girl won't need it too. When the teacher is teaching them numbers in K and a year later when they start basic addition she will probably be way past that and bored out of her mind. Anyhow, different differentiationed instruction, but still a need for it for both of them.
And while I don't want to give the non-english speaking parents comment much attention, I do want to say that they should all be part of the same class and they are by no means bringing other students down. Children pick up the English language quite quickly and they can be enriching other children's experiences in the classroom and teaching them things. They also are just as likely to be HG+ and need differentiation as well. Putting them in a seperate location would not be beneficial for anyone as you learn things more through exposure.
