Being rather new to schooling....my son just turned five, so I have only very recently started looking into stuff, I don't know much about what common core is..although I know there is a lot of angst about it, but I am not sure why.
But from what I can tell there is a lot of repetition. I.e. while double digit adding will be covered in second grade, they might not to triple digit until third...even though the principle is exactly the same and seems to me that it would make sense to do it all at one time. Another example - they introduce Roman numerals in first grade, but only cover up to 10, second grade goes up to 100, and third up to 9999. Again, there is a lot of repetition. Each grade seems to do a lot of the same thing, only slightly increasing the level of complexity. While it is probably good to go over things that are only rarely used (roman numerals) in math on a yearly basis to keep it in your head, I don't see the point of covering one topic so incompletely - why can't a child do three digit adding if they can do two? I don't know if that answers your question. I think they figure that each subject needs something like seven repetitions for the average learner...can't remember where I heard that "statistic".
They do the same thing with time starting with basic time concepts of before, after, morning, noon and night, am and pm (then to the hour and half hour one year, quarter hour and 5 minutes the next, and to the minute the following year, and finally time problems using elapsed time). It appears to me that each year they review the previous knowledge to be able to move on to the next level of knowledge.
