You can check the current years Entrance exam paper along with the answer sheet at: https://www.sainikschooladmission.in/Pdf/6th_A.pdf The question paper has Mathematics, GK, Language and Intelligence test. The question paper has 4 sections.

Section A has 50 Mathematics questions for 3 marks each

Section B has 25 GK questions for 2 marks each

Section C has 25 Language questions for 2 marks each: You can select the language

Section B has 25 Intelligence questions for 2 marks each

If your son is appearing for 6th class exams, he has to be well versed upto 5th standard Mathematics. The language should be of his comfort and knowledge and not your interest. That way he can score better. GK is learnt by reading News Paper regularly and Manorama book. There is no other way out for this. Intelligence section can be practised by previous model papers available in the market.