def flesch_kincaid_grade_level(n_syllables, n_words, n_sents):
    """
    Readability score used widely in education, whose value estimates the U.S.
    grade level / number of years of education required to understand a text.
    Higher value => more difficult text.

    References:
        https://en.wikipedia.org/wiki/Flesch%E2%80%93Kincaid_readability_tests#Flesch.E2.80.93Kincaid_grade_level
    """
    return (11.8 * n_syllables / n_words) + (0.39 * n_words / n_sents) - 15.59