I am not familiar with the Sages-2. Have you seen this document which describes the subtests?
http://www.prufrock.com/Assets/ClientPages/pdfs/sages/CH01-SAGES-2.pdf
It sounds like the reasoning portion measures "problem solving" skills that make it sound more like an IQish test and the other sections are more of an achievement section.

Does the school give this test to everyone or just kids that they suspect may be gifted? I am wondering if the teacher is seeing something that makes him/her think that he might be appropriate for a gifted program. You mentioned dyslexia. He may be twice-exceptional with his dyslexia suprressing his acheivement.