<p>I don’t seem anything at all wrong with mentioning achievements in ECs, if you happen to have some.</p>
<p>Having achieved something in connection with an EC is one form of evidence of your commitment to it. If you qualified for all-state band, for example, that’s evidence of the degree of your commitment to playing the trombone. </p>
<p>But maybe you could tweak your explanations a bit to emphasize your interest and commitment (I prefer this word to “passion,” which sounds idiotic to me) rather than focusing exclusively on the results. For example, “One of my longstanding interests is playing the trombone. During high school, I have had the chance to play with my school’s wind ensemble and marching band, as well as in X and Y outside organizations and the all-state honors band” might make a better impression than “Of the 85 people who tried out for the trombone slots in the all-state honors band, I was one of three who qualified.”</p>