
    In an adaptive learning platform, develop a function that calculates the total number of successful mastery demonstrations (indicated by even scores) from follow-up retention exercises (located at even positions) in a student's assessment sequence. This measurement helps evaluate the consistency of concept retention across practice sessions.
    

    
def sum_even_and_even_index(arr):
    """
    In an adaptive learning platform, develop a function that calculates the total number of successful mastery demonstrations (indicated by even scores) from follow-up retention exercises (located at even positions) in a student's assessment sequence. This measurement helps evaluate the consistency of concept retention across practice sessions.
    

    """
def sum_even_and_even_index(arr):
    """
    In an adaptive learning platform, develop a function that calculates the total number of successful mastery demonstrations (indicated by even scores) from follow-up retention exercises (located at even positions) in a student's assessment sequence. This measurement helps evaluate the consistency of concept retention across practice sessions.
    

    """
    i = 0
    sum = 0
    for i in range(0, len(arr), 2):
        if arr[i] % 2 == 0:
            sum += arr[i]
    return sum