This study aimed to examine authentic models of science assessment in assessing the competence of senior high school students who met the criteria of validity, practicality, and effectiveness. The methodology applied was an evaluation and developmental research. Research was conducted in senior high school in accordance with the needs of the development of authentic Statistical Analysis System (SAS) models. The participants were students of class X senior high school Gowa in South Sulawesi academic year 2020/2021. The instruments comprised (1) SAS model validation sheet; (2) science achievement test; (3) questionnaires; and (4) observation sheet. The findings of the quality authentic science assessment model met the validity and effectiveness criteria for high category learning outcomes with positive student responses. The practicality implications of the SAS model were also very worthy of applied science in teaching science for assessing the competence of senior high school students.