This study aimed to develop a valid and reliable instrument that measures the functional vision of students with low vision. Thus, an assessment tool and performance activities were developed for three vision skill groups (near vision skills, distance vision skills, and visual field) that include functional vision skills. The universe was 1485 students studying in various primary and middle schools (from 2nd to 7th grades) affiliated to the Ministry of National Education, and simple random sampling was used to select 310 students. The data were collected using the Gazi Functional Vision Assessment Instrument developed by the researchers. Many-facet Rasch model and generalizability theory were used for the rater reliability of the measurements obtained from the instrument, while discriminant analysis was used for the validity of the measurements. The analysis showed that the measurements were reliable, and the inferences based on these measurements were valid. Thus, this instrument can be used to identify and assess the functional vision status of students with low vision.