How to use case in stored procedure..

ALTER proc [dbo].[spGetStudentFormative]
 @intStudentID int,
 @intMasterClassID int
 as
 begin
 select
         intSubjectId
      
         ,max(case when strEvaluationTerm = 'Evaluation I ' then strSubjectName end) Subjects
           ,sum(case when strEvaluationTerm = 'Evaluation I' then decMaxMarks end) Out_of
            ,sum(case when strEvaluationTerm = 'Evaluation I' then decObtainedMarks end) Marks_of_Skills
           ,sum(case when strEvaluationTerm = 'Evaluation I' then decPercentage end) Percentage
          ,max(case when strEvaluationTerm = 'Evaluation I' then strGrade end) Grade
           ,sum(case when strEvaluationTerm = 'Evaluation II' then decMaxMarks end) Out_of
            ,sum(case when strEvaluationTerm = 'Evaluation II' then decObtainedMarks end) Marks_of_Skills
           ,sum(case when strEvaluationTerm = 'Evaluation II' then decPercentage end) Percentage
          ,max(case when strEvaluationTerm = 'Evaluation II' then strGrade end) Grade
          ,sum(case when strEvaluationTerm = 'Evaluation III' then decMaxMarks end) Out_of
            ,sum(case when strEvaluationTerm = 'Evaluation III' then decObtainedMarks end) Marks_of_Skills
           ,sum(case when strEvaluationTerm = 'Evaluation III' then decPercentage end) Percentage
          ,max(case when strEvaluationTerm = 'Evaluation III' then strGrade end) Grade
          ,sum(case when strEvaluationTerm = 'Evaluation I' or strEvaluationTerm = 'Evaluation II' or  strEvaluationTerm = 'Evaluation III' then decMaxMarks end) Out_of
          ,sum(case when strEvaluationTerm = 'Evaluation I' or strEvaluationTerm = 'Evaluation II' or  strEvaluationTerm = 'Evaluation III' then decObtainedMarks end) Total_of_Formatives
     ,sum(case when strEvaluationTerm = 'Evaluation I' or strEvaluationTerm = 'Evaluation II' or  strEvaluationTerm = 'Evaluation III' then decPercentage/3 end) Percentage
     ,max(case when strEvaluationTerm = 'Evaluation I' or strEvaluationTerm = 'Evaluation II' or  strEvaluationTerm = 'Evaluation III' then 
    (case when decPercentage>=91 and decPercentage<=100 then'A1' 
      when decPercentage>=81 and decPercentage <=90 then'A2'
     when decPercentage>=71 and decPercentage <=80 then'B1'
     when decPercentage>=61 and decPercentage <=70 then'B2'
     when decPercentage>=51 and decPercentage <=60 then'C1'
     when decPercentage>=41 and decPercentage <=50 then'C2'
     when decPercentage>=33 and decPercentage <=40 then'D'
     when decPercentage>=21 and decPercentage <=32 then'E1'
    else 'E2'end)end)Grade
   
   from vwStudentMarksStructure where (intMasterClassID=@intMasterClassID and intStudentID=@intStudentID)and intCategoryID in( select  intCategoryID from vwStudentMarksStructure  where (intMasterClassID=@intMasterClassID  and intStudentID=@intStudentID)and strDescription='Formative Assessment')
   group by intSubjectID
     end