Good Luck.
Think about all the things you would like to be seen done for your DS in terms of differentiation and discuss with principal how his need can be met even with a 1 grade skip.
As an example for DS, he is in an accelerated/gifted 2nd grade class. The class works out of 3rd grade reading and language arts books. DS can pick books out of the school library at his own reading level. For math, they were not able to coordinate schedules for him to go to 3rd grade for math, so he is working out of the 3rd grade book in his class. His teacher has agreed to pretest him each unit and move on if he has mastery of it. There are about 9 gifted kids in the class and they get pulled out for science enrichment 2x a week. This has helped in the science area being able to explore at a much higher level. Math is still not prefect and we will see how it goes this year. He learns math at such a fast pace that one grade of math a year will not satisfy him, but we found a class locally (well 40 min away) that has approaches math through logics and he is really enjoying it. He gets to use negative numbers and multiplication. The teachers at the math enrichment have had other DYS and during the initial assesment for placement saw him abilities immediately. So for now he is enjoying learning again.
The other thing is that there are still a lot of basics that he is learning especially with grammer and writing, even though he could be going ahead he is learning that he needs to pay attention in class more so that he picks up on some of the basics. He realized on Friday that he missed a question on his reading/language arts test because he was not paying attention when his teacher was going over what a fragment is compared to a sentence. That in itself was a learning experience for him, it is the first time he realized that he missed something he needed to know because he was not paying attention.

For now it is good enough and we will see as he goes forward when changes will need to be made again. The school was also honest enough to let us know that they may not be able to meet his needs through 5 grade. Another skip or homeschooling may be needed in a few years. We will see.

For now it is important that you think about what you can ask of the school to meet his needs. Further assesment of his math level may be needed and how can his school accomodate it.

The one good thing is that your school seems to have acknowledged that he has special needs and it will be a matter of working with them to see that those needs are met.