Does Istikhara inform one of success in exams or of the total score achieved?

Istikhara does not reveal future events, nor does it determine a person's success or failure. It is recommended to be optimistic and proactive, to have a good opinion of Allah Almighty, and to supplicate to Him through prayer; as Allah Almighty said in the Hadith Qudsi: "I am as My servant thinks of Me." It is cautioned against despair and supplicating against oneself; as the Prophet, peace and blessings be upon him, said: "Do not supplicate against yourselves, nor supplicate against your children, nor supplicate against your wealth; lest you coincide with an hour from Allah in which He grants supplications and He responds to you."