Average level of achievement (4)
I believe the answer is:
norm
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">average level of achievement</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for norm that I've seen before include "Usual or standard thing" , "Mean" , "Something typical" , "Typical, usual" , "Average level of achievement" .)