I think if I were you, I'd start narrowing the options for moving to a single school district (or maybe 2, if you're really ambitious). You don't need to find the house, but decide on an area. Then you can start researching schools now, while there's time to make decisions. The more you can do early, the better chance you have of finding something that will really work for B.
Are you going to buy or rent the next place? Do you have a real estate agent or rental agent yet? If not, I'd say get one and start asking questions about schools. I don't think they're allowed recommend anything specifically, but the one we had was very good at answering the question without saying any "wrong words." Be sure she knows about B's situation so that she doesn't just say, "Oh, yes, XYZ is a good school system." You need details about GT ed! That they are allowed to offer you.
Then you could put B in the new school starting at the beginning of the year and not even have to worry about the school he is at now.
Have you tried getting B to write a book for others to read? That helped my DS with his writing more than anything. If it's writing designed for others, he makes more of an effort. It may not work, but it's something else to try.
Some of it is just age. He's 5! 5yos don't write very well. There's not a lot that can be done about that. By next year, he may show vast improvement just by virtue of his aging a year. <shrug> I'd fight hard against keeping him in 1st if the only concern is his writing.
Have you gotten the IAS for him, to see if grade-skipping is recommended? I think it is, but it's worth having the test to get the official seal of approval...
