That's a very good question, and it looks like many parents are beginning to rebel against these "standards." The latest NCTE newsletter cites an article in The New York Times about how many New York parents are delaying the age their children begin formal schooling. Here's a link to that article:
It seems that the standards are beginning earlier and earlier in an attempt to change our status among international countries...this is especially true in the areas of math and science. The kindergarteners will probably be tested using images and graphs instead of words in order to get a handle on their basic knowledge skills.
Testing 5 year olds with bubble sheets is definitely a bad idea. Kids this age do not understand the purpose of standardized tests. They also are going to be put under undue stress if they do realize what the test is for!