Calculating Score Difference between oldest and newest score

Point Increase = 
// 1. Identify the earliest and latest dates for this specific student
VAR EarliestDate = 
    CALCULATE (
        MIN ( TestScores[date_taken] ),
        ALLEXCEPT ( TestScores, TestScores[student_name] )
    )

VAR LatestDate = 
    CALCULATE (
        MAX ( TestScores[date_taken] ),
        ALLEXCEPT ( TestScores, TestScores[student_name] )
    )

// 2. Retrieve the Composite Score on the Earliest Date
VAR EarliestScore = 
    CALCULATE (
        MAX ( TestScores[Composite Score] ), 
        ALLEXCEPT ( TestScores, TestScores[student_name] ),
        TestScores[date_taken] = EarliestDate
    )

// 3. Retrieve the Composite Score on the Latest Date
VAR LatestScore = 
    CALCULATE (
        MAX ( TestScores[Composite Score] ), 
        ALLEXCEPT ( TestScores, TestScores[student_name] ),
        TestScores[date_taken] = LatestDate
    )

// 4. Calculate the difference
RETURN
    LatestScore - EarliestScore

If you place student_name into a Table or Matrix visual in your report, a Measure is much more efficient. A measure does not consume memory in your data model like a calculated column does. Because the visual itself automatically filters down to the specific student, you do not need the ALLEXCEPT function here.

Point Increase Measure = 
VAR EarliestDate = MIN ( TestScores[date_taken] )
VAR LatestDate = MAX ( TestScores[date_taken] )

VAR EarliestScore = 
    CALCULATE (
        MAX ( TestScores[Composite Score] ),
        TestScores[date_taken] = EarliestDate
    )

VAR LatestScore = 
    CALCULATE (
        MAX ( TestScores[Composite Score] ),
        TestScores[date_taken] = LatestDate
    )

RETURN
    IF (
        NOT ISBLANK(EarliestScore) && NOT ISBLANK(LatestScore),
        LatestScore - EarliestScore
    )

If this helped, please consider giving kudos and mark as a solution

@me in replies or I'll lose your thread