Central Board Of Secondary Education [CBSE] — Moderation of numbers

I am Aryan Agarwal student of Dr Maria Residential Academy Agra School code 60039. Sir I have very low marks in accountancy and economics due to which my total percentage has suffered. I have scored 90percent marks in 10 and also Have performed very well in my class 11 & 12. The school says your marks have been moderated by cbse. What is the Basis of moderation policy where below average students score 85-90 percent and brilliant and aspiring students preparing for IIT and CA are given below average marks. Also favourite students of teachers top the school.
I request board officials to look into the matter ASAP as I am unable to concentrate on my further studies seeing the result