You can look at what topics are included in the math curriculum in each grade, or you can look at what kinds of problems students in various grades are able to answer correctly. NAEP results were released recently, and a few sample questions are at http://www.joannejacobs.com/2013/11/nations-report-card-scores-inch-up/ , and lots of sample questions are at the NAEP site http://www.joannejacobs.com/2013/11/nations-report-card-scores-inch-up/ . You can also Google phrases such as "california math tests" to get questions from NCLB-mandated state tests.