No, not quite. In your example, scoring at the 87th percentile with 30/30 correct means about 13% of first graders scored 30/30 on the reading. Percentile ranks indicate what proportion of the norming group had scores that were lower than the test taker. So a percentile rank of 90 means that 90 percent of the norming group scored the same or lower on the test, percentile rank of 50 means that half of the norming group did the same or worse. A score at the 95th percentile is in the top 5% of performance with respect to the norming group.
[My emphasis.] Unless you're making a nice terminological distinction that I'm not understanding, that doesn't quite make sense, aculady. In the case of 30/30 being reported as 87th percentile, it doesn't make sense to say that this means 87% of people scored
the same or lower - because obviously 100% of people scored the same or lower! The only interpretation that makes sense in that case is that (100-87)=13% of people scored
the same or higher (in this case that's the same as "scored the same" since there is no higher). The whole issue comes from the question of what is done with people who scored exactly the same as the person in question. Your quote above states both possibilities, but they do not give the same result. It's purely a matter of convention which is used, but for coarse measures one has to know, as it can make a big difference in interpretation.
