Welcome, NCmom!
My DS is currently in K in a Two-Way Immersion (TWI) (Spanish/English) program at our nearby public school. They start teaching 90% in Spanish and 10% in English in Kindergarten. And half the kids in the class are native Spanish speakers and half are native English speakers. My DS was probably about the same reading level (in English) as yours before entering K. We didn't test him on math, but he was definitely above K level before starting.
The first couple of months of the school year went well. DS was interested and engaged. However, he is now quite bored and starting to act out in school (talking while the teacher is, giving goofy answers to her questions, not paying attention, etc.). (We are implementing some new "respect" rules for school tomorrow -- we'll see how it goes...) We met with the principal and teacher a couple of weeks ago, urging them to accelerate some subjects for him. They have started sending home more difficult math homework and they are going to send him to the TWI 1st grade classroom for reading. So we'll see if those things help him.
All in all, I have mixed feelings at this point about his being in the TWI program. On the one hand, he can already read in Spanish (still working on the comprehension though) and is starting to speak Spanish without any accent! But his acting out behavior in school shows me that he is bored with where he is at.
I'm not sure if that's helpful, but perhaps hearing about someone's experience in one of these situations might help...
Good luck! And one thing I learned from the wonderful folks on this forum is that many solutions that work well are often only temporary. So what works for 6 months or 1 year, might not work for your DS in the next 6 months to a year. But there are always opportunities to switch gears as needed.
