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1. Introduction
National survey information indicated that the percentage of definite singleton children among married women has increased from 4.4% in 2006 to 7.8% in 2016. This increase in the singleton birth rate in Tehran is much higher than in other cities in Iran. Accordingly, the rate of actual singleton birth in Tehran between 2009 and 2014 has more than tripled from 3.6% to 11.9% [1].
Past developmental psychology kinds of literature have revealed noteworthy relationships between parenting styles and social, emotional, and behavioral proficiency of kids [2]. Anger is a basic emotion that it is known as popular phenomenon; aggression is any verbal or physical behavior that proceed from anger and it has intentional or unintentional destructive dimension; this behavior can be expressed to oneself or another object actively or passively [3]. But assertiveness as an another path to coping with stressful situation, is an adaptive communication style, through which people directly indicate their emotional state and desires, with keeping admiration to other people [4]. In other words, the term of assertiveness refers to raising a person to his/her rights with respectful conduct and words to others; it is also an exact, truthful, and proper method of describing one’s own emotions, thought, and beliefs [5]. On the one hand, a lack of assertiveness may contribute to many mental disorders, such as anxiety, depression, attention-deficit/hyperactivity (ADHD), and oppositional defiant disorder [6], while dysfunctional view to assertiveness could lead to aggressive behavior [4]. On the other hand, depression [7], social anxiety, self-belief [8], shyness, fear of negative evaluation [9], and personality characteristics [10] can influence the assertiveness.
The study of parent-child relationships and parenting styles is one of the most crucial discussions in psychology. Parenting is all efforts associated with the raising of children. Researchers have reported several human parenting methods, ways in which parents interact with their kids, with most classifications altering the dimensions of emotional warmth (warm vs. cold) and control (high-control vs. low-control). One of the most important of these arrangements is that Baumrind introduced [4]. Baumrind [11, 12, 13] basically recognized three parenting styles: authoritarian, permissive and authoritative; far along, Maccoby and Martin [14], retheorized a fourth rejecting–neglecting style [15]. These styles include four kinds of styles: authoritarian parenting, in which the parent or caregiver emphasizes obedience, deemphasizes collaboration and discussion, and applies potent forms of punishment; authoritative parenting, in which the parent or caregiver supports a child’s liberty but still sets particular boundaries on behavior; permissive parenting, in which the parent or caretaker is accepting and supporting, makes few requests and avoids using control; and rejecting–neglecting parenting style, in which the parent or caregiver is unsupportive, fails to observe or limit function, and is more attentive to its needs than those of the child [4]. The process of parenting is an essential element for the development of children. It contributes them in emerging the necessary abilities to function in and face society as adults [16]. Each style of parenting has a diverse impact on manners and character of the persons [15]. Styles of parenting are a series of combined performs that assist in regulating the people be opposed the environmental difficulties [17]. Proper parenting can contribute to optimal social functioning, and inappropriate parenting can lead to incompatible behaviors and difficulties in the future [16].
There are several studies on the relationship between styles of parenting and several psycho-social consequences among adolescents and children. For example, in a systematic review, Okunlola et al. [18] mentioned the relationships between self-esteem and the style of parenting they are perceived. Diaconu-Gherasim and Mairean [19] found that styles of parenting are correlated with goal directions and academic success among under 18-year-old teenagers. Scharf et al. [20] detected an correlation between moderately-high levels of affecting signs, such as depression, anxiety and up-raising scores of punitive parenting style. Smetana [21] also declared that punitive manners, like physical shrieking, condemnation, embarrassing, are a core feature of authoritarian style of parenting. Experiencing the parental verbal-form of aggression has associations with high scores of anxiety and depression symptoms [22]. An authoritative style of parenting reciprocally is associated with minor level of depression that maintains over time. The present study aimed to develop an explanatory model of assertiveness based on parenting styles mediated by anxiety and self-esteem.

2. Materials and Methods
This study is a descriptive-correlational modeling with partial least square. The statistical population included singleton children of the sixth grade of elementary school in the 3rd District of Tehran in the academic year 2017-18. Sampling method was multi-stage sampling; eight schools (four all-boys and four all-girls) were randomly selected from all primary schools in the 3rd District of Tehran; then a sixth-grade class was randomly selected in each school. The singleton students of those classes participated in the present study. The sample size calculation was performed by the G*Power software (effect size of 0.1, α=0.05, Power=0.95 and three predictors, n=110); accordingly, the sample size was 118 students (81 girls and 37 boys) and the mean age of the samples was 11.57 years. The inclusion criteria were being singleton child, being student, and being student in sixth grade of elementary in the 3rd district in Tehran. The exclusion criteria were having a psychotic disorder or having neurodevelopmental disorder according to demographic characteristic form that was completed with informed consent by parents of the participants.

Measures
Persian form of baumrind parenting scale 
For the first time, Diana Baumrind developed this questionnaire in 1972. It involves thirty items; each parenting styles contains ten items. This questionnaire measures parents’ opinions on a 5-point Likert scale. Therefore, parents are asked to choose an alternative that fits their current attitude very well. The spectrum includes fully agree, almost agree, disagree, rarely disagree, and completely disagree. Buri, quoted from Mahdavi [23] reported that the test-retest reliability of this questionnaire was 0.81 for allowance of, 0.92 for an authoritarian parenting style, and 0.92 for an authoritarian parenting style. In assessing the validity of this scale, he reported a ratio of tolerance to the authoritarianism of 0.50 and a ratio of authoritarianism to the authoritarianism of 0.52. In Iran, Esfandiari, quoted by Mahdavi [23] reported that the test-retest reliability was good for each styles (0.69-0.77).

Beck anxiety inventory (BAI)-Persian form
BAI is a widely used self-assessment scale for assessing anxiety symptoms developed by Beck et al. [24]. BAI has 21 items on a 4-point Likert scale. BAI has excellent internal consistency (α=0.92) and excellent test - retest reliability (r=0.75). It was slightly correlated with rHDRS (0.25) and moderately correlated with rHRAS (0.51). In Iran, the findings of Kaviani and Moosavi [25] showed that the Iranian version of BAI had upright reliability (r=0.72), high validity (r=0.83), and admirable internal consistency (α=0.92).

Persian form of Rosenberg self-esteem scale (RSES) 
It is a 10-point scale developed by Rosenberg [26]. The RSES is a one-dimensional scale that measures both positive and negative emotions towards oneself in order to achieve comprehensive self-esteem. All items are answered using a 4-point Likert scale from “completely agree” to “completely disagree”. The RSES is generally very reliable questionnaire. The test-retest correlation is in the very good range (r= 0.82 to 0.88), and the Cronbach’s alpha for different samples is in the range (α= 0.77 to 0.88). The Persian form of RSES [27] has suitable psychometric characteristic. The correlation between the total score of the item (r= 0.42 to 0.73) and the reliability of the alpha supports the internal consistency of the scale (α=0.83). The test-retest reliability showed the stability of the score (r=0.84), and the correlation between the scale score and the reference scale suggested the simultaneous validity of the scale. Factor analysis of the Rosenberg scale confirmed its one-dimensionality (ml=0.63).

Adaptive and aggressive assertiveness scale (AAAS)
AAAS is a self-assessment scale. The AAAS contains 19 items that represent common interactive situations that can describe oneself. Assertiveness answers are categorized by setting. Half of the items reflect the adaptive assertive response and the other half reflect the positive assertive response. The participants show how well they respond to each agreed (1=never, 5=always). AAAS showed suitable reliability for Cronbach’s alpha (α=0.82) and test-retest (r=0.81). The AAAS Persian-form confirmatory factor analysis also identified two factors, adaptive self-assertion subscale and positive self-assertion (KMO =0.75). Cronbach’s alpha coefficient is an acceptable coefficient for self-assertion (α=0.71) and aggression (α=0.72) subscales.

Procedure
Initially, in coordination with the university’s research affairs, researchers obtained permits and administrative considerations for entering the schools and conducting the research. Before presenting the questionnaire to the sixth graders of an elementary school in the 3rd District of Tehran, the first researchers introduced the study with brief explanations about the purpose of the research. Those participated in the study gave full oral informed consent and expressed their opinion and information about the confidentiality of the answers was given to the participants. Informed consent, demographic forms, and the study questionnaires were individually provided to students and then, they and their parents completed them at home without any time limitation for completing the questionnaires.
Data were analyzed in statistical package for social sciences (SPSS 26) and SmartPLS-3 software.

3. Results
Descriptive statistics 
Table 1 illustrates the mean, standard deviation, kurtosis, and skewness of the variables of the study.

The descriptive characteristics of the variables of the study are illustrated in Table 1. The mean of parenting styles was 17.6±4.28, 23.33±6.03, 14.43±4.48, respectively for the authoritative, permissive, and authoritarian parenting styles; these statistics were 19.88±4.94 for anxiety, 24.8±3.10 for self-esteem, and 35.42±6.04 assertiveness. The results of the kurtosis and skewness column also show that all variables had a normal distribution. All statistics ranged from 2 to -2.
Table 2 illustrates the summarized results of goodness of fit indices for the measurement model.

Structural equations modeling (SEM) findings
SEM is a method for assessing the impacts of the predictive variables on criterion variable(s) of the proposed model. According to Hair [28], SEM has two steps, the first one is the assessment of factors of the model, and the next is assessing the structural model. For testing the variables of the model, researchers conduct the confirmatory factor analysis that indicated that the proposed model had proper fit (Table 2). According to Hair [29], standardized root mean square residual (SRMR), squared euclidean distance (SED), geodesic distance (GD), normed fit index (NFI), and root mean squared residual covariance matrix (RMS_Theta) indices are proficient of recognizing a scale of model misspecifications [30, 31]. According to the SEM findings displayed in Table 3, the hypothesized proposed model with six variables was found acceptable.

Convergent validity
The prime state for convergent validity is that the standardized factor loadings should all be significant (T>1.96) with a value of more than 0.50 [32] except for the authoritarian parenting styles. Findings in Table 3 indicate the t-values for the factor loadings that all exceed 1.00 (P<0.01). All factor loadings were greater than 0.90 confirming excellent convergent validity for the constructs of the present research.

Composite reliability (CR)
The CR column data indicated that the composite reliability was suitable with a recommended value more than 0.70 [33]. Accordingly, all constructs showed a CR higher than 0.70. The results also confirmed the average variance extracted (AVE) measure for any of constructs to be higher than the recommended threshold of 0.50 [34]. These findings indicated excellent CR, or construct reliability for the constructs used in this research. Table 4 illustrates the correlations and square roots of the AVE.

Discriminant validity
Fornell and Larcker [34] suggest that AVE should be higher than the correlations of the variables in the model. Accordingly, the AVE values confirmed the discriminant validity [34]. Therefore, discriminant validity was established for the constructs in the proposed model. The next stage in SEM is the calculation of the structural model. The structural model was tested; hence, the satisfactory measurement model was confirmed (Figure 1).

After obtaining the fitness of the measurement model, the estimated coefficients of the causal relationships among constructs were examined.
Figure 1 demonstrates the path model with standardized factor loadings. Accordingly, Table 5 shows the direct, indirect, and total effects of determinant variables on predicting the assertiveness.

The results of Table 5 indicate that authoritative and permissive styles had a significant effect on assertiveness among the parenting styles. The total effect column means that authoritative and permissive parenting styles explained 0.22 and -0.20 of the variances of assertiveness; the results also showed that the authoritarian parenting style had no significant effect on assertiveness.

4. Discussion
The present study aimed to develop an explanatory model of assertiveness based on parenting styles mediated by anxiety and self-esteem. According to the findings of the present study, the suggested model was acceptably fit. Authoritative and permissive parenting styles had direct and indirect effects on assertiveness. These findings are in line with the findings of Bartholomeu et al. [35], Sochukwuma et al. [36], Alayi et al. [37], and Gauvain and Huard [38], but not with Un [39] and Sankah [40].
Un [39] showed that parenting styles alone did not have a significant impact on assertiveness. Accordingly, Sankah [40] reported that parenting had no effect on the assertiveness of adolescents. On the other hand, Gauvain and Huard [38], Bartholomeu et al. [35], and Sochukwuma et al. [36] noted that parenting styles had associations with assertiveness. Gauvain and Huard [38] reported that children with permissive, authoritative, and uninvolved parents originated more preparation negotiations in teens than children with commanding parents. According to the findings of the present study, the authoritative and permissive parenting styles have had direct and indirect links with assertiveness but authoritarian parenting styles were not associated with assertiveness. Assertiveness in the family environment had positive impacts on the children’s psychological well-being. The assertiveness with confronting, includes defending own rights and opinions and is associated with resistance to group pressure, stating self-esteem, even at the risk of a negative reaction from the other [41]. To explain these findings, we can state that the responsiveness (supporting and accepting) component of the parenting process is the core indicator for assertiveness. These address that children who developed in the families by low demanding and high responsiveness levels have more assertiveness in comparison to children of families with high demanding and low responsiveness parenting styles. Bamrind [42] stated that parents of socialized children with self-esteem have more authoritative parenting styles. Parent’s skills and behaviors are crucial in children development and are imperative in each part of children’s lifespan. The intimate relations among parents and their progenies, could lead to high self-esteem of children. These help children avoid more criminal activities such as substance abuse during adolescence. The assertiveness training packages have encouraging impacts on children’s self-esteem [37]. MacCord [43] stated that higher demands of parents lead to non-social adaptability. This is considerable when adding the impact of anxiety to this equation. High-demanding parents with hostile–coercive parenting behaviors try to control the behaviors, emotions, and cognition of their children, which increases their anxiety. These are related to the progress of problematic teenagers’ manners. These parenting behaviors include punitive disciplinal strategies, including arguing, yelling, hitting, spanking, or criticizing. Aggressive parenting can also contain utilizing culpability and humiliation to alter children’s misconduct or relying on paternal or maternal authority to prepare progenies obey inquiries or demands. Ordinarily, this parenting style is managed inconsistently. Parents are usually reluctant to punish or scream at their kids for each misconduct. In addition, parents tend to rely solely on habitual insensitivity when other tactics show their incompetence or they frequently become frustrated. Therefore, this parenting style has the strong correlation with anger and grievances [44].

5. Conclusion
We conclude that the authoritative and permissive parenting styles could affect assertiveness. According to Baumrind’s theory, parents’ warmth and responsiveness dimension play a crucial role in the development of their children’s assertiveness in the socialization process.
This study has some limitations; for example, the present study was performed on singleton students in the sixth grade of the regular elementary schools in District 3 of Tehran. Therefore, we should be aware of the generalization of these results to students of other educational grades, other cities, and students with other psychological, physical, and family statuses, such as students with special needs or students with siblings. We propose the future researchers perform this study again in different situations with various children. Finally, we suggest that educational officials, psychologists, and families use the results of this research. According to the negative impacts of anxiety on assertiveness, performing prevention programs that help to control anxiety and increase assertiveness is necessary among students.

Ethical Considerations
Compliance with ethical guidelines
All ethical ideas were considered in this article. All participants were informed about the purpose of the test and its steps. They were also confident in the security of their statistics and free to leave the examination whenever they want, and if they wish. They know that the results of the studies can be made public. Informed written consent has been obtained from individuals.

Funding
This study was not funded by public, commercial, or non-profit grantors.

Authors' contributions
All authors similarly participated in preparing this article.

Conflict of interest
The authors declared no conflict of interest.


Acknowledgments
We would like to acknowledge the contribution of the participants and all those assisted us to conduct the present study.


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