Cognitive interventions in children and adolescents from low socioeconomic status backgrounds: a systematic review protocol of randomized controlled trials

According to the United Nations (UN) [1], multidimensional poverty affects approximately 1300 million people around the world. Consequently, this number of people living with sub-optimal access to health services, educational opportunities, and daily life facilities needed to achieve a minimum level of well-being. Living in exclusion conditions has consequences related to quality of life in terms of lack of food, inadequate living conditions, and many other negative factors. Such conditions tend to support the perpetuation of poverty through successive generations [2]. Of those that suffer from multidimensional poverty, it is estimated that half are children [3]. Of note, childhood poverty is not a specific condition of developing countries considering that one out of five children living in developed nations experiences vulnerable conditions [4]. Childhood poverty is a complex phenomenon in that it is not just related to economic factors. It also involves elements that affect children’s well-being, such as lack of stimulation, overcrowded homes, lower parental education, and high levels of parental stress or anxiety [5], among others factors. Nevertheless, low familial Socioeconomic Status (SES) is associated with the emergence of childhood poverty. SES indicators refer to different factors such as family income, parent occupation, or parental education [6]. Family SES affects children’s lives in complex ways with the period of time living in poverty conditions being one important factor that impacts on their well-being [7]. In relation to this, many studies have shown how SES influences the adequate fulfilment of processes related to physical, emotional, and cognitive development [8, 9]. Additionally, low-SES is associated with malnutrition [10, 11]. According to the United Nations Children’s Fund (UNICEF) [12], globally, poor nutrition negatively impacts the development in one out of every three children. Worldwide, around 50 million children are considered underweight for their height and around 149 million children suffer from developmental delays [13].

Focusing on cognitive development, defined here as the maturational process through which children develop abilities and strategies to adapt themselves to changeable settings, it has been shown that living in poverty conditions can have a negative impact in cognitive domains [14]. Cognitive domains involve processes allowing an individual to perceive and organize internal and external information. These mental activities include perception, attention, memory, language, and executive functions. Executive functions have been widely studied [15] and encompass those mental activities related with information management and the exhibition of goal-directed behaviours: response inhibition, cognitive flexibility, working memory, planning, reasoning, self-monitoring, and the like. From previous literature, it is known that the brain systems which show the greatest anatomical and functional differences in children as a function of their SES are those related to language and executive functions [16‐18]. The efficiency in managing these complex cognitive activities can predict aspects related with academic performance [19], which is a key factor in determining a child’s life outcomes. In relation to this, children who live in disadvantaged conditions tend to underperform in school in comparison with their wealthier counterparts [7, 20]. Consequently, these children suffer a disadvantage in their academic lives from an early age.

From a global perspective, international initiatives such as those proposed by the United Nations in the 2030 Agenda through the Sustainable Developmental Goals (SDGs) are aimed at eradicating the differences that poverty causes around the world [21]. In relation to this, and in order to help overcome the difficulties that children from low-SES have in their cognitive performance, a number of different interventions and programs have been proposed and applied. Due to the nature of the disadvantaged context, intervention processes can be influenced by many factors. The heterogeneity of these factors could make it difficult to establish a “gold standard” intervention that leads to meaningful improvements in the cognitive domains of these children. Nevertheless, it has been demonstrated that implementing multi-modular programs that include significant agents and contexts could benefit different cognitive processes as well as providing benefits in other important areas of these children’s lives, such as in emotional and academic domains [22‐24].

Diverse intervention studies have been conducted in order to determine if the negative effects that low-SES settings have on children’s development can be alleviated. These interventions usually involved the children being assessed prior to the intervention and assessed for a second time once the intervention had concluded. This design enables improvements due to the intervention the children’s performance or behaviour to be identified. Accordingly, it is recommended that pre-post evaluations be carried out using standardized evaluation tools to allow the child’s performance to be compared with his reference group in terms of age, gender, etc. In this regard, cognitive interventions correspond to systematic actions designed and implemented by professionals in order to compensate or enhance cognitive functions. Furthermore, Bronfenbrenner [25] states that structured interventions designed to improve children’s cognitive skills may be considerably more effective compared with other less-structured interventions, especially when applied in a relevant context such as in the school curricula.

Of note, it is important to remember that at-risk children are influenced by many agents and context. Thus, a broad intervention program should include actions which target these diverse factors. These types of multi-modular programs include, for example, actions within the family context and educational initiatives, along with health-related interventions. A large number of such multicomponent intervention programs to improve disadvantaged children’s health and performance in, for example, cognitive and behavioural domains have been reported [22, 24, 26, 27]. Additionally, some researchers have studied the importance of implementing programs aimed at improving children’s development through indirect factors such as nutritional status [28‐30], physical activity [31], and applying programs which target a specific cognitive domain [32].

Another important factor to consider is whether the implementation is individual, or is carried out in a group setting. The individual format is appropriate in cases in which the researcher or the clinician desires to specifically adapt the intervention to the person. Consequently, it is useful to look for subtle enhancements or nuances in the child’s responses. This kind of intervention requires a greater investment of time and material, along with human capital, in order to be totally centred on the child’s potential and necessities. In contrast, a group setting allows the intervention to be implemented in less time, and with a lower investment of personnel and materials. Moreover, group settings may resemble the school environment in which children are immersed in a daily-basis, and thus recreate a more familiar environment for the child. Within the literature, there is evidence of both individual [33] and group [34, 35] interventions applied in order to enhance vulnerable children’s cognitive processes. For example, Segretin et al. [36] compared both individual and group cognitive interventions applied to 4-year-old vulnerable children reporting that the children participating in the group setting improved their performance in memory and planning processes, whereas the intervention using individual sessions was more effective in terms of attentional outcomes.

Previous literature exists which aims to offer a comprehensive analysis of cognitive interventions applied to vulnerable children and adolescents. For instance, Hermida et al. offered a compendium of intervention programs based on developmental psychology and cognitive neuroscience [23]. These authors pointed out further considerations that may be important when designing an intervention program to promote disadvantaged children’s cognitive development, such as the importance of considering the developmental cognitive neuroscience and the need to work on basic cognitive processes. Moreover, in her synthesis, Warr-Leeper [37] offered a description of early intervention programs that have shown effectiveness in this at-risk population. This synthesis included a comprehensive review of well-known programs, the vast majority of which were conducted in the USA that aimed to alleviate the negative impact that living in disadvantages settings has for children’s development. Some examples of the programs reviewed are as follows: Head Start Program [38], Carolina Abecedarian Project [39], Project CARE [40], and Syracuse University Family Development Research Program [41]. These programs are characterised by the fact that they include diverse services in order to meet the children’s needs as completely as possible. Health services, parenting programs, and family support are some of the benefits that participating families were able to receive. Research studies conducted within the framework of these programs demonstrated improvements in the cognitive development of the children who participated, except in the case of the Syracuse University Family Development Research Program [41], in which children showed a better socioemotional performance, but did not show improvements in cognitive performance [37].

Furthermore, there are also systematic reviews of intervention programs whose goals were to enhance the development of children specifically from low-SES settings. These reviews have focused on different aspects, including parent-centred interventions [42], interventions designed around home-visits [43], home-based programs [44], programs focusing on improving nutrition [28], and interventions centred on a specific cognitive domain; for instance, language stimulation [45]. Moreover, a systematic review undertaken by Kathib et al. [46] suggested the importance of interventions implemented in early childhood in order to ensure a healthy development in low and middle-income countries. A very recent study conducted by Saitadze and Lalayants [47] has offered a compendium of mediation mechanisms that may modulate the negative effects that poverty-associated factors have in children’s cognitive and emotional outcomes. These authors have pointed out that having proper stimulating material and an adequate parental support could cushion the impact poverty has on childhood development.

Focusing on linguistic outcomes, Heidlage et al. [48] conducted a meta-analysis of parent-centred interventions in low-SES children. In contrast, the goal of Scionti et al.’s systematic review [49] was to assess the efficacy of cognitive training focused on executive functions in pre-schoolers with low-SES and ADHD. Furthermore, due to the important role that parents play in early childhood, some studies have promoted children’s development through parental intervention [45, 50].

Considering all of the factors in these studies shown to be associated with improving low-SES children’s development, it is not difficult to imagine the great heterogeneity of results within the field. The paediatric population includes a wide range of ages in which important changes are presumed to occur in different areas of children and adolescents’ lives. This is just one possible source of heterogeneity that may exist in the studies that aim to enhance cognitive development through interventions. Depending on the age and cognitive outcomes in which researchers want to specifically work on, interventional studies will potentially be completely different. Another possible source of variability in terms of methodologies is the design and implementation of the study, as interventions conducted in relatively wealthy regions or countries are likely to have more and better resources than studies conducted in developing regions. That is, the political and social contexts in which a study is implemented will almost certainly impact on many factors of the study [36].

With regard to methodologies, implementing a full and well-conducted randomized controlled trial (RCT) may be difficult to implement with disadvantaged populations. Although this type of design is recommended in order to determine the efficacy of an intervention, its implementation does involve some design considerations. RCTs require more time to implement, as well as more economic and human resources to be conducted (e.g., more research staff are needed to evaluate and implement the intervention to avoid bias). Furthermore, this type of study has ethical implications in the health area (e.g., to withhold effective interventions to participants in the control group in order to meet the research goals). Given the difficulties with low-SES environments previously described, some authors have used quasi-experimental designs [34, 35, 51, 52] to implement cognitive interventions, as implementing a full experimental design can be difficult.

Although the previously mentioned reviews provide valuable insight to advance the field, there are some limitations. For example, some reviews did not adhere to standardized guidelines [23] and others did not offer a comprehensive perspective focusing on interventions designed to enhance cognitive development in low-SES children [48]. Additionally, most of these reviews focus on the study of different types of interventions to enhance children cognitive development, but they did not focus on the interventions themselves. Consequently, since the authors of this protocol were not able to locate a systematic review that answers the research question: which cognitive interventions have been used to enhance the cognitive development of children and adolescents from low-SES setting using a RCTs design?, they decided to conduct a systematic review to fill this gap in the field.

The Cochrane handbook for Systematic Reviews of Interventions [53] was used to design the protocol and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols (PRISMA-P) [54] was followed to describe the protocol. The systematic review protocol was registered in the International Prospective Register of Systematic Reviews PROSPERO (http://​www.​crd.​york.​ac.​uk/​PROSPERO) on 16 March 2020 with the registration number CRD42020150238.

Worldwide, approximately 650 million children live in poverty or low-SES conditions. Low SES has been shown to negatively influence processes related to physical, emotional, and cognitive development [8, 9]. Thus, interventions designed to improve cognitive development in children living in low-SES conditions would potentially greatly benefit these children [62]. Nevertheless, to the best of our knowledge, no systematic review of such studies has been previously undertaken. Consequently, we set out to design a protocol for performing such a review.

The protocol described here contributes to the field considering that it is: (1) including literature regardless of year of publication, (2) assessing risk of bias of the studies through a standardized tool, (3) taking into account a wide age range in the populations who participated in interventions, (4) including interventions in any type of cognitive domain, which will give to the reader a comprehensive understanding of the field, and (5) only including RCT studies, which are the gold standard to test intervention efficacy. Furthermore, any systematic review based on this protocol would offer a comprehensive approach for a population that could benefit from an intervention undertaken by experts and agents involved in childhood developmental issues.

Among other strengths, the systematic review will offer results obtained through a methodical search in diverse databases. Moreover, review authors will hand-check the relevant literature contained in the references and other sources of interest.

Nevertheless, one limitation of the study is that the inclusion criteria are quite wide (e.g., age: children from 0 to 17; interventions undertaken in any cognitive domain). Thus, the selected studies will probably be heterogeneous, and consequently, it may be difficult to assimilate the data in order to undertake a quantitative analysis. Due to this possibility, the objective of the protocol will be to offer an al alternative approach which does not require the quantitative comparison of studies. Another limitation of this review could be the exclusion of studies using other kind of methodologies (that is, non RCTs designs), as other designs could be also be suitable for assessing the outcomes of interest. Although the quasi-experimental methodology is widely used in this field of study, it will be excluded by this protocol as we are interested in including the most robust, reliable studies in the review. Accordingly, the systematic review may be missing effective cognitive interventions for children from low-SES settings. Nevertheless, the inclusion of other kinds of methodologies could be considered as an extension to the proposed protocol to fully understand what has been effectively implemented so far.

The systematic review will be useful as it will offer a framework based on evidence, to organisations, institutions, and experts who want to implement or promote interventions aimed at enhancing cognitive domains in children and adolescents who live in disadvantaged contexts. Consequently, this study could inform interventions and policy settings, such as those that need to achieve the Sustained Developmental Goals (SDGs) about children education included in the 2030 Agenda. The fact that the systematic review will be composed only by RCTs will support the conclusions based on effectiveness criteria, capital aspect to policy decision making. This review will also provide researchers with a summary of what has proven to be effective depending on various intervention factors and sample features, offering future lines of research in the field where debate is still open.