Hello aspirant,

Those who did not perform well in their board exam, and hence, could not get the desire marks, such student can apply for the improvement of marks for those students who are glooming because they think their copies were not checked properly,  and therefore,  want their.answer sheet checked again, can apply for re_evaluation or re_checking so this is.the basic difference between improvement and.re_checking

Hope you understand, 
Thank you