Seniors: You can still send new scores and other materials after the application deadline
It is very important that colleges receive all the documents that they require before the application deadline so that your application is flagged as complete, otherwise it will not be considered. But just because the deadline has passed, you may still send new or follow up materials. If you have not yet received a decision from the college, it is possible that the new material may be considered even if sent after the deadline.
Anything that would increase your odds of acceptance should be sent. For example, you were elected captain of a sports team, you won a poetry contest, etc. A special case of this is new standardized test scores.
Score reporting for standardized tests often occurs around the various deadlines for early action, early decision, rolling admission and regular admission. Delays in ACT or SAT reporting scores to the colleges are common, even weeks after the scores are known to you. If you are in a situation like this, you should take a screen shot of your new scores and send that to the college, with a note informing them that you have ordered an official score report which should arrive soon. Send the screen shot immediately, the same day that your scores are posted on the ACT or SAT web site.