<p>One way a college can learn about your scores even if you do not send official scores is that many high schools put all your scores on your official high school transcript so you better check what yours does.</p>
<p>Also, there are colleges, beginning with entry clas of 2010, which will require you to provide all your scores if you apply, both SAT and ACT.</p>
<p>Barring one of the above, you can avoid reporting the score when applying to many colleges.</p>
<p>You can avoid your school sending the ACT score by not including the HS code when you sign up (assuming things have not changed since my daughter was taking the ACT 2 years ago)</p>