NCE scores, or Normal Curve Equivalent scores, are a method of reporting test scores created for the US Department of Education. They range from 1-99 with a mean of 50, similar to percentiles. However, unlike percentiles, NCE scores maintain equal interval and can be meaningfully averaged and differenced.
The graphic below shows how NCE scores compare to percentiles. The NCE scores are evenly spaced while the percentiles are not. The graphic also shows that an NCE score of 50 is equivalent to the 50th percentile, but an NCE of 74 is equivalent to about the 90th percentile. This means that a student with an NCE score of 74 performed better than 90% of other students. On the other end of the spectrum, the graphic shows that a student in the 20th percentile would have an NCE score of about 33.