From
http://ags.pearsonassessments.com/group.asp?nGroupInfoID=a32215 :
Scores/Interpretation: Age- and grade-based standard scores (M=100, SD=15), age and grade equivalents, percentile ranks, normal curve equivalents (NCEs), and stanines
I've never seen test scores written in this manner using "sum." I've never seen raw scores released to a parent, so I'm thinking the scores are Scaled Scores. Additionally, it appears the Reading subtest scores make up the overall reading score. For instance, if fluency is a part of the reading coomprehension problem, it's something that needs to be specifically targeted in her IEP.
With a mean of 100, 100 is dead on average. The standard deviation is 15, so low-average would be 85 (100-15); high-average would be 115 (100+15).
Scaled Scores can be converted to:
Reading Standard Score (m=100, sd=15) 75
T Score (m=50, sd=10) 33
scaled score (m=10, sd=3) 5
z -1.67
Percentile 5
Written Expression Standard Score (m=100, sd=15) 73
T Score (m=50, sd=10) 32
scaled score (m=10, sd=3) 5
z -1.80
Percentile 4
This tells me that your child has reading and written expression lds. I'd want additional testing in order to target specific weaknesses -- see the "new" test in the table with-subtests and composites at he web address above.
Understanding Tests and Measurements for the Parent and Advocate at
http://www.wrightslaw.com/advoc/articles/tests_measurements.html will be helpful for you.