I think my DD's old 1st grade teacher said it best when we met at the 1st parent teacher meeting. " I have 22 kids in my class: 4 of them should still be in kinder, 12 of them are doing well for 1st grade, 4 of them are at 2nd grade level, 1 of them is at 3rd grade level reading and 1 is reading at middle school level and doing Math at 4th grade level."
She was awesome. She tried to differentiate according to the kids' abilities. Some parents who are 1st grade level (in both reading and Math) complained to the principal (not getting enough attention and accused the teacher of favoring the smart kids) and she stopped after about 4 months.
You should check the school. But even in the same school, the teachers (especially elementary) have flexibility to teach what they deemed necessary. But most will be cookie cutter teachers and will teach only the curriculum. Common core curriculum is here..
http://www.corestandards.org/ELA-Literacy/RI/1/
