Introduction
Adolescents with Autism Spectrum Disorder (ASD) experience difficulties such as limited social participation, lack of belonging, reduced quality of life, school failure, challenges transitioning to adulthood and independence, executive function difficulties, and problems entering the workforce (1-8).
Given these challenges, self-determination is an important developmental construct in this population. Self-determination is a combination of skills, knowledge, and beliefs that enable individuals to engage in goal-directed and self-regulated behavior. Understanding one’s strengths and limitations, along with believing in oneself as capable and effective, is essential for self-determination. When individuals act according to these skills and attitudes, they gain greater control over their lives and are more likely to become successful adults in society (9).
Reliable assessment of self-determination is necessary for identifying strengths and needs, monitoring progress, and planning educational or therapeutic interventions. The Self-Determination Student Scale (SDSS), developed as part of the Self-Determination Assessment Battery, assesses cognitive and emotional aspects of self-determination(10).
Since its development, psychometric properties of the SDSS have been assessed in different cultures and populations. The SDSS has since been translated into Slovenian, Arabic, and Persian and the reported Cronbach’s alphas were acceptable (0.90, 0.95, and 0.79, respectively) (11-13). However, the test–retest reliability of the Persian SDSS has not been examined in adolescents with ASD. This gap is important because adolescents with ASD may differ in self-reflection, item interpretation, and response consistency, which can influence the stability of self-report measures. Therefore, the present study aimed to examine the test–retest reliability of the Persian version of the SDSS in Persian-speaking adolescents with Level 1 ASD.

Materials and Methods  
Study design
This methodological study evaluated the test–retest reliability of the Persian SDSS. The scale was administered to the same participants on two occasions, 14 days apart, to assess the stability of scores over time.

Participants and setting
Nineteen Persian-speaking adolescents aged 13–18 years with Level 1 ASD were recruited by convenience sampling from three rehabilitation and occupational therapy centers in Tehran. Therapists at each center identified adolescents who appeared to meet the eligibility criteria and informed their parents about the study. Interested adolescents and parents received information about the study purpose, voluntary participation, confidentiality, and the two assessment sessions. Written informed consent was obtained from both adolescents and their parents before data collection.
Eligibility criteria included age between 13 and 18 years, documented diagnosis of Level 1 ASD, and ability to complete the Persian SDSS with clarification if needed. Level 1 ASD was determined based on documented clinical diagnosis by a child psychiatrist and available Gilliam Autism Rating Scale–Third Edition (GARS-3) assessment records. The research team did not independently reclassify ASD severity. Adolescents with documented comorbid psychiatric diagnoses or major medication changes during the test–retest interval were excluded. The absence of comorbid psychiatric diagnoses was determined from documented medical history available at the participating centers and parent report during recruitment. No standardized diagnostic interview was conducted by the research team to independently assess comorbidities. No formal priori sample-size calculation was conducted. The sample size was determined by the number of eligible and consenting adolescents available across the participating centers during the data collection period. Therefore, the findings should be interpreted as preliminary.

Instrument
The Self-Determination Student Scale (SDSS) is a self-report measure developed as part of the Self-Determination Assessment Battery to assess cognitive and emotional aspects of self-determination. In the present study, the revised Persian version of the SDSS was used, excluding items 1, 17, 28, and 87, as recommended in the Persian psychometric study. Therefore, the administered version included 88 items. The SDSS contains two-option items: “That’s not me” and “That’s me.” According to the scoring key of the Self-Determination Assessment Battery, each item has a keyed response. If the participant selects the keyed response, the item receives the score assigned to that response: 1 point for “That’s not me” or 2 points for “That’s me.” If the participant does not select the keyed response, the item receives 0 points. Therefore, because keyed responses may receive either 1 or 2 points depending on the item, the total score is not limited to the number of items, and scores above 88 are possible. Higher total scores indicate higher self-determination.

Procedure
The SDSS was administered twice with a 14-day interval. Both administrations were conducted in quiet and controlled rooms at the participating centers. Participants were allowed to ask for clarification when needed; however, clarification was limited to explaining item wording, and no answers were suggested by the researchers or parents.
All 19 participants completed both administrations, and no participant dropped out between test and retest. Data completeness was checked before analysis. No missing item responses were found, and all 19 participants were included in the ICC analysis.

Statistical analysis
Data were analyzed using SPSS version 26.0. Descriptive statistics, including mean, standard deviation, minimum, and maximum, were used to summarize SDSS scores across the two administrations. Test–retest reliability was evaluated using the Intraclass Correlation Coefficient (ICC), because the SDSS produces quantitative total scores and the aim was to estimate agreement between two administrations of the same instrument.
A two-way mixed-effects model with absolute agreement for single measures was used. Single-measures ICC was reported to reflect reliability at the individual participant level. ICC values above 0.90 were interpreted as excellent reliability (14).

Ethical considerations
Ethical approval was obtained from the Ethics Committee of Iran University of Medical Sciences (IR.IUMS.REC.1401.478). Written informed consent was obtained from adolescents and their parents before participation. This study was a methodological reliability study and did not involve intervention allocation; therefore, clinical trial registration was not applicable.

Results
Nineteen eligible adolescents were enrolled in the study. All participants completed both the first and second administrations of the SDSS; therefore, no attrition occurred between test and retest. No missing item responses were recorded, and all 19 participants were included in the final ICC analysis. Participant characteristics are presented in table 1. All participants were Persian-speaking adolescents with Level 1 ASD recruited from three rehabilitation and occupational therapy centers in Tehran.
Descriptive statistics for SDSS scores across the two administrations are shown in table 2. The first administration produced scores ranging from 37 to 126, while the second administration produced scores ranging from 38 to 124. The mean total scores were very similar across the two administrations, indicating no major group-level shift between test and retest. However, individual-level stability was evaluated using ICC rather than descriptive statistics alone.
Before ICC calculation, the dataset was checked for missing responses, scoring inconsistencies, and data-entry errors. The mean difference between the second and first administrations was 0.42 points, showing minimal average change across the 14-day interval. As shown in table 3, the single-measures ICC was 0.998, with a 95% confidence interval of 0.996–1.000. This result indicates excellent test–retest reliability of the Persian SDSS in the present sample.

Table 1. Participants characteristics

Table 2. Descriptive statistics of self-determination scores across two measurement occasions

Table 3. Intraclass correlation coefficient results for test-retest reliability

Discussion
This study examined the test–retest reliability of the Persian version of the SDSS in Persian-speaking adolescents with Level 1 ASD. The findings showed excellent temporal stability over a 14-day interval, with a single-measures ICC of 0.998. This result suggests that, in the present sample, SDSS total scores remained highly consistent when the scale was administered twice under similar conditions.
The high ICC observed in this study should be interpreted carefully. The dataset was checked for missing responses, scoring inconsistencies, and data-entry errors before analysis. The very small mean difference between the first and second administrations suggests minimal average change across the test–retest interval. However, the exceptionally high ICC may also reflect the relatively wide between-participant variability compared with small within-participant changes. Therefore, this result should be viewed as preliminary evidence of temporal stability rather than proof of broad psychometric adequacy.
The findings are consistent with previous psychometric work suggesting acceptable reliability of the SDSS in other populations and cultural adaptations(11,13,15-19). The Persian SDSS had previously been evaluated in adolescents with emotional–behavioral symptoms, but its test–retest reliability had not been examined in adolescents with ASD. The present study adds initial evidence for the stability of the revised Persian SDSS in this specific population. Reliable repeated assessment may be useful when researchers or clinicians need to monitor self-determination scores over time, but only within the limits of the evidence provided here.
Several limitations should be considered. First, the sample size was small, and participants were recruited by convenience sampling from three centers in Tehran, which limits generalizability. Second, only adolescents with Level 1 ASD were included; therefore, the findings may not apply to adolescents with Level 2 or Level 3 ASD. Third, comorbid psychiatric diagnoses were excluded based on documented medical history and parent report rather than standardized diagnostic interviews, so undetected anxiety, ADHD, depression, intellectual disability, language disorder, or learning disorder may have been present. Fourth, the SDSS is a self-report measure, and responses may have been influenced by self-reflection difficulties, item interpretation, recall, or response bias. Finally, this study examined only test–retest reliability. Other psychometric properties, including internal consistency, construct validity, concurrent validity, responsiveness, and measurement error, should be examined in future studies.
Beyond its psychometric significance, the reliability of the Persian SDSS has practical implications. Recent research emphasizes that assessing self-determination provides a foundation for improving functional and developmental outcomes in autistic youth (20). Higher levels of self-determination have been associated with improved transition readiness, increased participation in community and school activities, and better quality of life (21,22). In this context, a reliable assessment tool enables clinicians and educators to identify strengths and needs more accurately and to design occupation-based and person-centered interventions that target meaningful life goals.
Overall, the findings provide preliminary evidence that the revised Persian SDSS has excellent test–retest reliability in a small sample of Persian-speaking adolescents with Level 1 ASD. Larger studies with more diverse samples are needed before broader clinical, educational, or research use can be recommended.

Conclusion
This study provides preliminary evidence of excellent test–retest reliability of the revised Persian SDSS over a 14-day interval in a small sample of Persian-speaking adolescents with Level 1 ASD. The findings support the temporal stability of SDSS scores in this specific sample, but they should not be generalized to all adolescents with ASD. Further studies with larger and more diverse samples, including adolescents with different ASD severity levels, are needed to examine additional psychometric properties such as internal consistency, construct validity, concurrent validity, responsiveness, and measurement error.

Acknowledgement
Ethical approval was obtained from the Ethics Committee of Iran University of Medical Sciences (IR.IUMS.REC.1401.478). The authors extend their gratitude to the participants for generously contributing their time to complete the assessments. This study was part of the corresponding author’s Master’s dissertation.

Conflict of Interest
There was no conflict of interest in this manuscript.