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<p>The test was probably too hard if all of the scores were compressed to the bottom end of the scale. One test in a frosh level course I had managed to hit what is probably the ideal score distribution for “curve” grading: min = 0, max = 100, median = 50 (or very close), and a close to uniform distribution.</p>
<p>In any case, back to the original question, it is not unusual for graduate and undergraduate students to be in some of the same courses, as the graduate students may be in undergraduate courses to “make up” course work that they may not have taken as undergraduates, while advanced undergraduate students may be in graduate courses.</p>