Question: Do You "Flex?"

A question (followed by quite a few more): are you a kindergarten teacher who "flexes" or utilizes grade level "flexible grouping?"

If so, HOW?  An hour?  Half an hour?  Math and Reading?  Centers or didactic/teacher led instruction?  Small group, large group, aides, volunteers, school specialists?  How long does it take for your students to get into the groove of moving (smoothly) between multiple ever-changing classrooms at the beginning of the year?  Do your groups REALLY change, or are your highest kids always your highest requiring enrichment and your most needy always behind the curve year-round?

Seriously, I'd love to know!  Plusses, pitfalls, pros and cons.

You know how I feel about developmentally appropriate practice, so just put that on the back burner if need be, and share what you've experienced when you've assessed and grouped at this age level.  Thanks so much for any and all information you can share!