This study was conducted with the aim of comparing the effect of acceptance and commitment therapy and self-compassion on cognitive flexibility in anxious female students of the second year of high school. The research method was semi-experimental in two stages: pre-test and post-test. In this study, 30 people were selected through convenience sampling and randomly assigned to two experimental groups and one control group (10 people in each group). Then the experimental groups underwent 8 sessions of acceptance and commitment and self-compassion therapy, and the control group did not receive any therapy. Anxiety questionnaire and cognitive flexibility scale were used to collect data. Data were analyzed using multivariate analysis of covariance. The results showed that in the post-test stage, there is a significant difference between the acceptance and commitment and self-compassion treatment groups compared to the control group in increasing cognitive flexibility. Also, the results showed that there is no significant difference between the two treatments of acceptance and commitment and self-compassion in terms of effectiveness on psychological flexibility. Based on the findings, both acceptance and commitment therapy and self-compassion are suitable options for increasing cognitive flexibility in anxious female students of the second secondary level. IntroductionOne of the psychological injuries and pressures that teenagers are exposed to is anxiety (Sattari & Erfani, 2019). Anxiety is related to cognitive flexibility. Cognitive flexibility refers to the ability to switch between strategies in a flexible way that usually takes place in response to changes and conditions (Clarke & Kiropoulos, 2021). It is also defined as the ability to maintain strategy and efficiency in the presence of distractions, which is impaired due to anxiety )Clarke & Kiropoulos, 2021; Park & Moghaddam, 2017; Zare & Baradaran, 2019(. Therefore, treating these problems is very important. Third-wave treatments such as acceptance and commitment therapy (Kelson et al., 2019; Zare, 2017) and self-compassion (Heidari et al., 2023; Shafieifar et al., 2022) are among the key interventions to treat anxiety symptoms. Acceptance and commitment therapy employs processes such as mindfulness, acceptance and commitment to increase psychological flexibility to help people with anxiety symptoms (Mahmoudfakhe, 2022). In the self-compassion approach, instead of criticizing themselves for their shortcomings and flaws, people support themselves and accept themselves unconditionally (Saadatmand et al., 2022). Since the third-wave treatments have been highly regarded by researchers and psychologists, comparing such treatments might be beneficial in several ways. For example, people pay a material and spiritual cost when receiving psychotherapy. Therefore, they should receive treatment that is more effective for their problem. As such, the current research seeks to compare the effectiveness of acceptance and commitment therapy and compassion-focused therapy for the cognitive flexibility of female students with anxiety symptoms in the second year of high school. MethodThe current research design was quasi-experimental with a pre-test-post-test design with a control and experimental group and a 3-month follow-up. The statistical population consisted of all female students in the second grade of high school in Mahabad, Iran. Among the statistical population, one school was selected via the random cluster sampling method. In the next step, the selected school was referred to and 350 questionnaires were distributed among the students of that school, and finally, 30 students with anxiety symptoms were randomly assigned to two experimental groups (acceptance and commitment group and self-compassion group) and one control group. Then, the experimental groups received the acceptance and commitment treatment protocol (Hayes, 2008) and the compassion-based treatment protocol (Gilbert, 2009) for eight sessions (each 90 minutes). The research tools were: the Beck Anxiety Questionnaire (1991) and Dennis and Vander Wal's Cognitive Flexibility Questionnaire (2010). Descriptive statistics (mean and standard deviation) and inferential statistics including repeated measurement analysis of variance were used to analyze the collected data. ResultsBefore running the analysis of variance test with repeated measurements, its presuppositions were checked. Shapiro-Wilk test was used to check the normality (p>0.05) and the assumption of normality of the data was confirmed. Box's M test confirmed the equality of the variance-covariance matrix in the desire to understand difficult situations (Box's M=33.13 , F=2.30 , p=0.06>0.05), the ability to understand several alternative explanations (Box's M=25.67 , F=1.78 , p=0.054>0.05), and the ability to create several solutions(Box's M=24.17 , F=1.68 , p=0.06>0.05). The assumption of sphericity was confirmed through the Mauchly test for the desire to understand difficult situations (Mauchly=0.633 , p=0.030.05). Also, these results showed that the post-test and follow-up have significant differences in each component compared to the pre-test. ConclusionThis study was conducted with the aim of comparing the effect of acceptance and commitment therapy and self-compassion on cognitive flexibility among female students with symptoms of anxiety in the second high school. The present study found that both treatments had the same effect on cognitive flexibility in people with anxiety. These results were consistent with the findings of other studies (Coto-Lesmes et al., 2020; Heidari et al., 2023; Kelson et al., 2019; Shafieifar et al., 2022). In explaining the results, it can be mentioned that one of the definite consequences of anxiety is the disorder in cognitive flexibility. Cognitive flexibility is the ability to switch between strategies in a flexible way that usually takes place in response to changes and conditions, and it is also defined as the ability to maintain strategy and efficiency in the presence of distractions, which is impaired due to anxiety. In this regard, acceptance and commitment therapy can reduce the symptoms of disorders through different strategies such as increasing attention and awareness, acceptance and letting go, being in the present moment, desensitization, observation without judgment, and desensitization. This therapy helps people to make changes in their dimensions when needed and to accept and adapt to an uncontrollable event. Also, through the strategy of mindfulness, people can focus on their current goals and ignore the factors that cause interference. Students participating in this research were able to separate themselves from unpleasant thoughts and events by placing themselves as context. Also, these people can learn how to let go of the central processes that caused intellectual inhibition. In other words, this treatment with behavioral commitment exercises and determining values and goals led to an increase in flexibility in students with anxiety symptoms.On the other hand, self-compassion includes suitable coping resources through which it can help people face the conditions and situations that are accompanied by anxiety. This approach puts a lot of emphasis on mindfulness. Mindfulness allows people, especially students, to focus their minds on the present moment and be aware of current stimuli, which leads to the development of cognitive flexibility. This therapy teaches people to accept themselves unconditionally, as a result, people may not try to change anything and adapt to the situation more easily. According to the mentioned cases, the treatment of self-compassion and acceptance and commitment have similar processes to reduce anxiety. Some of these processes include mindfulness, acceptance and creating a new relationship with oneself, thoughts, experiences and feelings. In other words, there are common features, goals and benefits between both treatment methods. Therefore, it is possible to justify the same effect of acceptance and commitment and self-compassion treatments on cognitive flexibility in students with anxiety symptoms.The current study has some limitations. For example, the sample was limited to female students in the second grade of high school in Mahabad, Iran. Also, the study relied mainly on the use of self-report tools for the variable of cognitive flexibility, which may provide superficial information and be associated with favoritism. Considering the limitations, it is suggested that this study be conducted with males, other age groups, clinical and non-clinical groups, and in other cities. It is suggested that third-wave treatments be compared with first and second-wave treatments regarding their effectiveness for psychological flexibility. At the practical level, it is also suggested that due to the same effect of methods based on acceptance and commitment and self-compassion, the necessary platform for the implementation of these methods should be created in schools. Ethical ConsiderationCompliance with Ethical Guidelines: All ethical issues such as confidentiality of participants' identity were attended to and informed consent were obtained from the participants.Authors’ Contributions: All steps of the article are done by the author of the article.Conflict of Interest: The authors declare no conflict of interest for this study. Funding: The authors received no financial support for the study. Acknowledgment: The authors would like to thank all participants for their time and contribution to the study.