but am I right in thinking there is no testing required in this instance in the US and there is zero enforcement?
If you're fully vaccinated then no, you don't need to do daily tests, so no, there's no enforcement of the daily tests here.
But if they did want to see the results of daily tests then the enforcement would be not letting the student attend school without the daily test results, or not letting the employee attend work without the daily test results.
Not sure if that answers your question?