<p>Yes, there is attrition, but rising initial interest can still mean that post-attrition enrollment is higher than anticipated.</p>
<p>For example, CS courses have experienced a rapid rise in interest in recent years:
<a href=“CS106A enrollment reaches record high”>http://www.stanforddaily.com/2012/10/04/cs106a-enrollment-reaches-record-high/</a>
<a href=“Stanford's summer introductory CS classes now require application for enrollment”>http://www.stanforddaily.com/2014/07/13/stanfords-introductory-cs-classes-require-summer-applications/</a>
(Stanford is not unique in this respect.)</p>