
    In an adaptive learning system, students complete pre-tests and post-tests for each module, with scores stored in ascending order. Given these paired assessment scores, where each student's pre-test and post-test scores appear twice except for one incomplete assessment score that appears only once, write a function to identify this single unpaired score that requires follow-up.
    

    
def search(arr):
    """
    In an adaptive learning system, students complete pre-tests and post-tests for each module, with scores stored in ascending order. Given these paired assessment scores, where each student's pre-test and post-test scores appear twice except for one incomplete assessment score that appears only once, write a function to identify this single unpaired score that requires follow-up.
    

    """
def search(arr):
    """
    In an adaptive learning system, students complete pre-tests and post-tests for each module, with scores stored in ascending order. Given these paired assessment scores, where each student's pre-test and post-test scores appear twice except for one incomplete assessment score that appears only once, write a function to identify this single unpaired score that requires follow-up.
    

    """
    n = len(arr)
    XOR = 0
    for i in range(n):
        XOR = XOR ^ arr[i]
    return XOR