We started worrying about DS5's kindergarten placement about the same time you did. However, a good piece of advice I got on this board was if you've found a current school situation that works, be happy, and don't worry too much about what happens next! (Easier said than done, I know.)
Thinking about your options...
1. You may find that by this time next year, DD has completely outgrown the school, and you'll easily be able to remove this option. Or, you may find the the teachers there really "get" her, and are willing to keep giving her something that challenges her. (Will she stay with her current teacher, like in a Montessori school? A great flexible teacher can make all the difference.)
2. Definitely an option, if you can make it work financially, but the school may not be willing. In which case options 1 or 3 would be best.
3. Talk to parents at the school. There may be options for differentiation within a regular classroom. A school, for example, can schedule math time for all of the primary grades at the same time, so you DD could move to another class during math. Any good primary teacher should be differentiating reading with guided reading groups.
As for our decision, we've decided to keep DS at his current Montessori school (that goes through the kindergarten year)...and in a sense "kick the can" until first grade. (At that point we'll have to decide public school vs. a Montessori that goes to sixth grade.)
