While Prince George's County pupils scored on the average above the national norm on standardized tests, the school system reported last week, the spread between averages by school was more than 70 percentile points.

Results of the California Achievement Tests showed that fifth-graders at Bond Mill Elementary School in Laurel averaged in the 94th percentile, the highest figure among county schools. The lowest percentile ranking for a grade level was at Glassmanor Elementary in Oxon Hill, where third-graders averaged in the 24th percentile. The national average is the 50th percentile.

The countywide average on the standardized tests has climbed 6 to 8 points above the national norm over the past four years. The tests were given to third-, fifth- and eighth-graders last fall.

Prince George's third-graders performed best in the language section of the test, in which they averaged 14 percentile points above the national norm. Their mathematics scores were 10 points above the national average, their spelling scores were 6 points above the norm, and their reading scores were 4 points higher than the national figure.

Fifth-grade pupils exceeded the national norm by 14 points in language, 10 points in spelling, 8 points in math and 3 points in reading. Eighth-graders exceeded the national norm by 11 points in language, 7 points in spelling, 6 points in mathematics and 2 points in reading.

At left are average percentile rankings by school: