Comprehensive assessment following national education standards that have been set is part of a teacher’s life as an education servant. In Indonesia, the 2013 curriculum is used reference and a guide for the learning process. The 2013 Curriculum is seen as having a complex complexity in terms of assessment. Teachers are explicitly asked to conduct balanced assessments of the cognitive, affective, and psychomotor domains according to objectives. This research aims to test the reliability of the authentic assessment instrument of learning outcomes of invasion game materials in elementary schools through product moments. This research was conducted in an upper-class elementary school in DIY with a sample of 48 people, both teachers, and students. The research method used in this study is a survey and uses a quantitative approach. The instrument used and tested for reliability is a Likert scale questionnaire. For data analysis in this study, reliability analysis was used based on the Cronbach alpha value with the help of the SPSS V.22 calculation application. The results showed that the reliability of each factor was based on the high Cronbach alpha value. The alpha value for teachers is 0.939, and the alpha value for students is 0.604. It can be concluded that the instrument used is reliable for what will be measured and has a high value which means it can measure the object. Authentic assessment instruments for elementary school invasion games can be used later as a helpful measuring tool.