Using Report Builder 3 Need to group fields from multiple input records

Creating a Report Builder 3 report where multiple records are read.  First set is Math records with a state Math total.  Next set of records are for ELA also with a State ELA total.   Creating report where on the detail line I place the fields for each record.  First 2 records for Math then 3 records for ELA.  On the total line for GRADE, I need to get the State MATH total in one column and the State ELA total in a different column.   Having problems when I use the expression =IIF(Fields!Subject_Name.Value = "MATH" ,(Fields!Num_Student_tested.Value),nothing).  Problem is the Fields!Subject_Name once it completes the read for this Grade is not = to "MATH" but = to "ELA".   Need to be able to pull the value from the detail line into the Total line just for MATH.   Attaching the report rdl
StateGradeReport.pptx
SRR2d.rdl