The study aimed to develop a criterion-referenced test to determine to what extent that grade five basic education students in Oman master spelling pattems of the Arabic language and to specify the appropriate cut-off scores for mastery decisions depending on their ability in spelling patterns. Moreover, the study investigated the psychometric properties of the mastery decisions based on the test scores. To achieve the aim of this study, the development of the test went through several stages: the test content was specified, behavioral objectives were analyzed, the test items were written according to Pophom standard test and descriptive validity was well measured. A pilot sample of 262 students from grades 3,4,5 was administered to obtain the initial psychometric properties of the test Then, the reliability and validity were examined. Using contrasting groups, the cut-off scores was determined to classify grade five stude abilities in Spelling patterns. The test was conducted to stratified sample of 999 students from Muscat region. The highest 50% of grade five students were assumed to be a mastery group and grades 3 and 4 students were assumed to be non mastery groups. Two cut-off scores were obtained from the total Spelling patterns score in addition to the other 31 behavioral objectives. The results revealed that the cut-off scores of the Spelling patterns were less than the common mastery level. The psychometric properties of the mastery classification decisions of grade five students were determined and the results showed that the test of Spelling pattems of the Arabic language had functional validity and high reliability.