This script loops BACKWARDS through a block of data, applying logic and noting which rows mandate a new row insert. It then loops through the collected "insert" rows, applying the final logic

insert_new_rows_based_on_values.vb

Option Explicit
Public Sub InsertNewRowsBasedOnValues()
    
    Dim wksData As Worksheet
    Dim lngLastRow As Long, lngIdx As Long, _
        lngStudentCol As Long, lngItemCol As Long, lngNetAmtCol As Long, _
        lngPreviousAmtCol As Long, lngNewAmtCol As Long, _
        lngReversalCol As Long
    Dim varRowNum As Variant
    Dim colRowNumsForInsert As Collection
    Set colRowNumsForInsert = New Collection
    
    'Set references up-front
    lngStudentCol = 1
    lngItemCol = 2
    lngNetAmtCol = 3
    lngPreviousAmtCol = 4
    lngNewAmtCol = 5
    lngReversalCol = 6
    Set wksData = ThisWorkbook.Worksheets("Sheet1")
    lngLastRow = LastOccupiedRowNum(wksData)
    
    'Loop through the data range BACKWARDS, tracking each
    'case where a row will need to be in a collection
    With wksData
        For lngIdx = lngLastRow To 2 Step -1
        
            'On every loop, we ALWAYS:
            '  1. set the New Amount value to the Previous Amount value
            '  2. set the Reversal to "Y"
            .Cells(lngIdx, lngNewAmtCol) = .Cells(lngIdx, lngPreviousAmtCol)
            .Cells(lngIdx, lngReversalCol) = "Y"
            
            'If the Net Amount is > 0, though, we also need
            'to note that row number so we can eventually add
            'a new row there
            If .Cells(lngIdx, lngNetAmtCol) > 0 Then
                colRowNumsForInsert.Add Item:=lngIdx, Key:=CStr(lngIdx)
            End If
        
        Next lngIdx
    
    
        'Nice! We have done a lot of data prep already -- we just need
        'to add rows where necessary and apply the right values
    
        'Loop through the row numbers in our collection, which
        'are conveniently in REVERSE order (as adding rows will
        'change the row numbers in the range, making forward looping
        'very difficult
        For Each varRowNum In colRowNumsForInsert
            
            'First, insert a new row, shifting everything below it down
            .Range("A" & varRowNum).Offset(1).EntireRow.Insert Shift:=xlDown
            
            'Write the Student and Item numbers (which are the same)
            .Cells(varRowNum + 1, lngStudentCol) = .Cells(varRowNum, lngStudentCol)
            .Cells(varRowNum + 1, lngItemCol) = .Cells(varRowNum, lngItemCol)
            
            'Write the New Amount (which is the Net Amount from the
            'row above)
            .Cells(varRowNum + 1, lngNewAmtCol) = .Cells(varRowNum, lngNetAmtCol)
            
            'Write the Reversal to "N"
            .Cells(varRowNum + 1, lngReversalCol) = "N"
            
        Next varRowNum
    
    End With
    
    'Let the user know the script is done
    MsgBox "Finished!"
    
End Sub

'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
'INPUT       : Sheet, the worksheet we'll search to find the last row
'OUTPUT      : Long, the last occupied row
'SPECIAL CASE: if Sheet is empty, return 1
Public Function LastOccupiedRowNum(Sheet As Worksheet) As Long
    Dim lng As Long
    If Application.WorksheetFunction.CountA(Sheet.Cells) <> 0 Then
        With Sheet
            lng = .Cells.Find(What:="*", _
                              After:=.Range("A1"), _
                              Lookat:=xlPart, _
                              LookIn:=xlFormulas, _
                              SearchOrder:=xlByRows, _
                              SearchDirection:=xlPrevious, _
                              MatchCase:=False).Row
        End With
    Else
        lng = 1
    End If
    LastOccupiedRowNum = lng
End Function