You gotta have one standard, as we're one country.
Not just one standard, but each standard is basic:
1) all should be able to speak, read, and write in a common language to foster good communication (it used to be english). Good communication fosters better trust.
2) understand civic responsibilities to participate in government, such as our representative democracy, including voting but extending to actually filling some of those rolls. It is a hardship sometimes, but it must be done.
3) Indoctrinate our youth into the understanding that we are all created equal. From the highest-paid executive to the lowest-paid laborer, we are all equals. This is a natural (or God-given, if you prefer) right. It is ok that some people have different skills, jobs, or roles, but at the end of the day, we are all equals.
4) Indoctrinate our youth so they understand "Equity" is the basis for unequal treatment: all evil societies in history have incorporated this ideology of "Equity," or un-equal treatment, including slavery (those plantation owners were sure convinced they were doing the right thing by 'helping' the slaves they owned because they were inferior and needed the guidance of ownership), Nazism (the blue-eyed blond hair Germans knew for certain they were doing the right thing by eliminating inferior bloodlines and would have a utopian society in the process), and current school and governmental philosophy (we are indeed doing the right thing by 'helping' those poor and inferior people under us so that we can create a better utopia)
Beyond these things, maybe basic math and science?
Not one standard, but these are very basic standards.