1. Introduction

Early language acquisition plays a pivotal role in shaping future academic success [1]. Disparities in language abilities begin to manifest by kindergarten and persist throughout a child’s academic journey [1-2]. Early vocabulary and oral narrative skills are particularly predictive of later reading comprehension and literacy levels [2]. These crucial language abilities are often influenced by socioeconomic status (SES). Children from lower SES households are disadvantaged as they experience fewer opportunities for conversational turn-taking, hear fewer words on average, and receive less child-directed speech from parents and their environment, compared with their more affluent peers [3-4].

Interventions aimed at narrowing the SES gap in language development vary widely in their approaches, particularly regarding parental involvement. There is ongoing debate among researchers regarding the optimal level of parental participation. Some studies advocate for teaching parents specific strategies as a cost-effective method to augment intervention compared to practitioner-led efforts alone [5]. However, concerns have been raised about the lack of long-term evidence and variability in parental motivation and consistency, which may lead to inconsistent outcomes [6].

This literature review focuses on three effective interventions designed to improve language acquisition and development in children from lower SES backgrounds. It seeks to uncover commonalities and implications across global approaches while presenting evidence supporting the effectiveness of parental involvement in these interventions.

2. Ts Home Visiting Curriculum

2.1. General Description

The 3Ts Home Visiting Curriculum (3Ts-HV) is a six-month intervention designed by the TMW Center for Early Learning and Public Health at the University of Chicago, specifically tailored for parents of children aged 13 to 16 months from lower SES backgrounds. This curriculum, consisting of 12 modules, emphasizes enhancing the home language environment by increasing caregiver knowledge. It focuses on three key principles: “Tune in,” “Talk more,” and “Take turns” [7].

2.2. Analysis of the Three Key Principles

The “Tune in” component of the curriculum focuses on equipping parents from lower SES backgrounds with foundational knowledge in child development. This includes understanding critical language acquisition periods, basic cognitive and linguistic development, and the concept of brain plasticity [7]. By addressing the knowledge gap that often exists in lower SES households regarding the importance of early language acquisition, this segment prepares caregivers to engage more effectively in the training process. Moreover, it encourages sustained application of the practices well beyond the end of the curriculum. After a six-month training period, caregivers were found to be significantly more knowledgeable than their control counterparts [7].

In the "Talk more" component, there is a strong emphasis on increasing the amount of language input directed towards the child, encouraging and guiding parents to incorporate a diverse range of words during interactions. Child-directed speech is highlighted as crucial for vocabulary acquisition, offering numerous models for learning new words and enhancing the development of lexical processing skills essential for vocabulary growth [8]. Child-directed speech, unlike speech overheard from adult conversations, actively supports language learning in children [9]. This component addresses the disparity where mothers from higher SES backgrounds engage more in child-directed speech with their children [2]. Conversely, parents from lower SES backgrounds often employ authoritarian parenting styles, characterized by directives and yes or no questions aimed at managing behavior rather than fostering dialogue, potentially hindering children's speech development [2]. Researchers observed that caregivers gradually integrated child-directed speech into their daily interactions, resulting in increased exposure to adult vocabulary for their children [7].

Research highlights that mothers from higher socioeconomic status (SES) backgrounds frequently employ speech strategies aimed at promoting conversation, thereby aiding children in acquiring essential skills for conversational turn-taking that align with specific language and cultural norms [2]. Conversely, mothers from lower SES backgrounds tend to use speech more to direct their child's behavior rather than to facilitate interactive dialogue [2]. This distinction underscores the critical need to equip caregivers with effective strategies that promote interactive communication, which plays a pivotal role in enhancing children's language abilities and fostering positive social interactions. In the curriculum's 'Take turns' component, particular emphasis was placed on cultivating conversational turn-taking skills, recognized as crucial for children's language development [7]. This approach facilitates a reciprocal exchange of language, thereby enhancing children's grasp of the pragmatic aspects of communication. Parents were provided detailed instructions to foster the reciprocal nature of language exchanges in everyday conversations. It was found that parents engaged in more conversational turn takings, used fewer directives, prohibitions and restrictions-all factors that can suppress young children’s desire to explore and develop language skills [7].

2.3. Effectiveness and Implications

The 3Ts-HV Curriculum has underscored the crucial role of involving parents from lower SES backgrounds in interventions aimed at enhancing language acquisition. As primary and most frequent communicators with their young children, parents are pivotal in shaping their children’s developing language abilities. Research has shown that increases in both the quantity and quality of language input by mothers can persist up to 38 months after completing the curriculum, indicating promising long-term results [10].

Initially an in-person approach, the TMW Center has gradually expanded its reach by partnering with public organizations, such as public libraries and museums, to support more families in need. They have also created an online version of the curriculum, designed to demand less time from parents, and available in both English and Spanish to improve accessibility. This version includes video-based lessons to expand their reach even further [11]. However, the most resource-intensive version involves knowledgeable home visitors directly engaging with parents in hour-long sessions. This approach can pose challenges for both families and providers, contributing to an attrition rate of 23.79% [7]. Strategies are needed to retain participating families over time and to track the sustained impact of the intervention on children’s language development longitudinally.

Moreover, while positive changes in parents are optimistic indicators of improvements in young children, the curriculum's age limit may limit its applicability to early toddlerhood. Future research should focus on adapting these interventions for older children who missed the early intervention window, considering the varied levels of resource access among disadvantaged families.

3. Too Small to Fail

3.1. General Description

The Clinton Foundation's initiative, Too Small to Fail, collaborated with the LaundryCares Foundation to encourage early learning initiatives in low-income communities via laundromats throughout the United States [12]. This intervention acknowledges that social interactions fundamentally shape literacy development within children’s everyday experiences. The initiative aimed to integrate literacy learning opportunities into various everyday contexts regularly encountered by families, by establishing language-rich environments in informal settings such as laundromats.

In neighborhood laundromats, designated spaces were equipped with books and signage that encouraged parents to participate in activities like talking, singing, and reading with their children while they waited. Librarians were available to provide personalized assistance and strategies to promote literacy engagement. They often used interactive activities that linked books to the laundromat environment, creating valuable opportunities for vocabulary enrichment and interactive conversations. The initiative's evaluation highlighted several positive outcomes, including a noticeable increase in conversations between children and their parents and enhanced adult participation in goal-directed activities [12].

3.2. Analysis

This initiative tackled the issue of access to literature and book exposure, which often disadvantages children from lower socioeconomic backgrounds [13]. Research indicates that the presence of books at home predicts reading skills more strongly than parental educational attainment [14], highlighting the disparity in access to books as a contributing factor to differences in literacy development among children from different socioeconomic backgrounds. Moreover, the initiative's approach of having a librarian guide during activities may be more effective than children reading alone at library resources. Librarians purposefully posed open-ended questions to children, resulting in observed increases in multi-word utterances, which may encourage parents to adopt similar conversational strategies at home.

The intervention also provides flexibility by integrating literacy activities into laundromat visits, eliminating the need for families to allocate separate time commitments. This approach is believed to enhance retention rates as families can engage whenever they visit laundromats. However, the lack of structured participation in literacy learning poses challenges for assessing long-term effectiveness. Furthermore, the initiative does not extensively address individual differences among children and families, potentially limiting its ability to tailor interventions to specific needs.

3.3. Implications

Parental and caregiver involvement in the intervention was inconsistent and not sustained over time. Children often participated in reading and activities independently or with peers at these locations. Parents occasionally engaged, interacting sporadically, or reading with their children. Adult guidance primarily came from on-site librarians rather than parents. However, parents may have indirectly learned from observing librarian interactions and been motivated to replicate these interactions at home.

It's worth noting that some families in these communities primarily spoke Spanish at home, which could have limited their participation in English-language activities [11]. Nonetheless, the intervention included "trusted messengers" within the local community to educate parents about the connection between laundromat activities and school readiness, yet the effects of this remain unexamined.

4. The STELLA Curriculum Intervention

4.1. General Description

Researchers in southern China implemented the 'Storytelling and Retelling and Higher Order Thinking in English Language and Literacy Acquisition' (STELLA) curriculum for first-grade elementary school children from lower SES families with limited English proficiency [15]. Over an 8-week period, participating children took home authentic English storybooks and structured lesson plans aligned with their regular school curriculum to engage with their parents. The intervention focused on developing oral language skills rather than purely on language code skills [15]. Activities included reading and listening to storybooks, singing English songs, collaborative writing, and playing games with parents.

4.2. Effectiveness and Analysis

The STELLA curriculum has demonstrated effectiveness in enhancing children’s vocabulary and improving their listening proficiency across various English as a Foreign Language (EFL) contexts [16]. This effectiveness is achieved through repeated story reading, which facilitates vocabulary growth by exposing children to words multiple times, supported by visuals integrated into the books used in this intervention [15,17]. Additionally, listening comprehension is fostered through repetition and paraphrasing, with repeated exposure to words at home and through structured activities at school, including singing English songs known for their repetitive and expressive nature [15].

Moreover, parental involvement can significantly influence children’s motivation to learn English, particularly in EFL contexts [18]. However, the positive impact of parental involvement depends on parents respecting their children’s individual learning styles; parental pressure can potentially undermine motivation [19]. While the specific extent of parental respect or pressure and its impact on motivation were not measured in this intervention, the “playing games with parents” component likely created a comfortable environment that deviates from traditional learning settings, and potentially enhancing engagement by making learning enjoyable and reducing the need for parental pressure.

Additionally, a control group of students, who were not instructed to involve their parents in these activities, was monitored. Although not required to participate, parents in the control group initially engaged but their involvement decreased over the 8-week period. This decline in participation could be attributed to several factors, including a lack of structured guidance to sustain their interest in the activities. In contrast, parents involved in the STELLA curriculum maintained sustained engagement throughout the intervention [15]. This underscores the importance of employing structured motivational tactics within the STELLA curriculum to maintain ongoing parental engagement, which may influence the child’s engagement levels as well. Qualitative data gathered from parents indicated high satisfaction with the literacy activities. They expressed approval of the curriculum and reported observing improvements in their children's English oral skills [15]. Some parents appreciated how the activities strengthened their bond with their children and enjoyed learning English together, anticipating continued positive and active engagement in the future, which could lead to lasting impacts on academic success. Results also suggested an increase in students' motivation to learn English. However, the long-term effectiveness of the intervention still requires further study. Additionally, there is a need to explore how the STELLA curriculum can be adapted to accommodate children at different grade levels with varying levels of English proficiency.

5. Discussion

The three interventions examined in this study effectively promoted language acquisition in children from lower socioeconomic status (SES) backgrounds. By specifically targeting children during the critical period of language development, these interventions adopted a strategic approach. However, this focus may overlook children outside the targeted age group who still need support. Future research should investigate methods tailored towards older children as well.

Parental involvement played a crucial role in enhancing children’s language acquisition by fostering a vocabulary-rich environment. Educating parents on methods to support their children can significantly enhance the effectiveness of these interventions. Therefore, sustained parental engagement is vital for the success of these programs, both in initial involvement and in maintaining progress at home. To increase awareness about the availability of these interventions, it is recommended to focus on outreach efforts in lower SES neighborhoods, which could help more families recognize the importance of language acquisition and encourage them to seek out these programs. However, it is crucial to acknowledge that not all parents may have the time or energy to fully participate in these programs due to their work commitments. Low-income parents often rely more on childcare and spend less time on direct educational activities with their children [20,21], which affects the effectiveness and maintenance of parental involvement, an issue that must be considered during implementation.

Moreover, the interventions studied require significant involvement from both parents and experts, suggesting that only a limited number of children can be targeted at a time due to resource constraints. One possible solution is to implement these interventions in classroom settings in lower SES neighborhood schools, providing group support to students and their parents during school time. Programs like 3Ts-HV and STELLA could be supplemented by community resources, such as the laundromats used in the Too Small to Fail initiative, to consolidate effectiveness.

6. Conclusion

This literature review highlighted three effective interventions aimed at enhancing language acquisition and development in children from lower socioeconomic status (SES) backgrounds. The findings underscore the importance of parental involvement in these interventions.

A possible limitation of this study is its primary focus on language acquisition interventions in English, which may not adequately address the diverse primary languages spoken in many lower SES households. Given globalization and increasing immigration, predominantly English-speaking countries should recognize that significant segments of the target population may speak other languages at home.

Future research should assess the proportion of non-English-speaking households in the target regions and determine the applicability of these English-based interventions across various languages. Additionally, exploring the feasibility of applying these interventions across multiple languages simultaneously could ensure inclusivity and meet the diverse linguistic needs of children from varied backgrounds.