Numerous studies describe the features of state EI programs, such as the characteristics of children and families referred, evaluated, and enrolled, and the kinds of services received,24,26 but very few examine outcomes using rigorous methodology sufficient for attributing causal impact to EI services. The vast majority of outcomes studies do not have a control or comparison group to measure against the group receiving Early Intervention services, relying instead on a single group’s pre-intervention and post-intervention data, and many use parent self-reports through surveys to understand child and family outcomes, rather than using direct assessments of children’s progress by trained observers.14 As one researcher put it, a major “challenge to assessing impact of EI services on child outcomes is the mandate that services be available to all children who meet eligibility requirements. Conventional experimental approaches are, therefore, unobtainable and unethical” (pp. 74–75).27 The studies that do employ treatment and control groups tend to examine specific programs unique to a particular community and often have small sample sizes, limiting generalizability.28,29 Another EI researcher has cited “a critical gap in the literature linking [EI] service use and functional outcomes” (p. 2),30 and still others have acknowledged “intense professional debate surrounding claims of the effectiveness of early intervention” (p. 320).G
Despite these limitations in the research, some consistent evidence has emerged from studies of EI programs, particularly those focused on children born low birthweight,C,D,H,I,J demonstrating that participation in services can boost children’s developmental trajectories. However, more rigorous studies, with comparison groups when possible and larger sample sizes, would be valuable to broaden the evidence base and determine the impact of Early Intervention on more diverse groups of infants and toddlers.
The research on EI does not focus on the impact of a specific state policy lever on child and family outcomes, although some correlational studies have examined whether state eligibility thresholds impact participation in EI, given that eligibility is one of the aspects of the program that states independently determine. The research and most recent available data on the effect of broader or narrower eligibility thresholds find mixed results.42,47,48,49,50 Despite positive correlations found in most studies, the research does not support a causal link between broader eligibility and greater participation or better child outcomes at the state level.
The research discussed here meets our standards of evidence for being methodologically strong and allowing for causal inference, unless otherwise noted. Each strong causal study reviewed has been assigned a letter, and a complete list of causal studies can be found at the end of this review, along with more details about our standards of evidence and review method. The findings from each strong causal study reviewed align with one of our eight policy goals from Table 1. The Evidence of Effectiveness table below displays the findings associated with Early Intervention (beneficial, null,ii or detrimental) for each of the strong studies (A through Hiii) in the causal studies reference list, as well as our conclusions about the overall impact on each studied policy goal. The assessment of the overall impact for each studied policy goal weighs the timing of publication and relative strength of each study, as well as the size and direction of all measured indicators.
Table 2: Evidence of Effectiveness for Early Intervention Services by Policy Goal
|Policy Goal||Indicator||Beneficial Impacts||Null Impacts||Detrimental Impacts||Overall Impact on Goal
|Parental Health and Emotional Wellbeing||Maternal Self-Confidence||D, H||Mixed
|Maternal Role Satisfaction||D||
|Optimal Child Health and Development||Cognitive Assessment Scores||A, B, C, D, F, G, H||Positive
|Behavior Assessment Scores||C||
|Maternal Report of Infant Temperament||D||
|Receptive Language Skills||E||
|Expressive Language Skills||E||
Parental Health and Emotional Wellbeing
Although many studies examine family and caregiver outcomes after participation in Early Intervention services for their infants and toddlers, most studies suffer from methodological weaknesses that preclude causal conclusions. For example, many studies draw on surveys that lack a control group, rely solely on parent self-report, have a small sample size, and/or may be vulnerable to self-selection bias.31,44 However, three strong studies measured some indicators of parent wellbeing.D,E,H
A 1988 experimental study examined the long-term results of an 11-session Early Intervention program that sought to offer mothers support as they adjusted to parenting a low birthweight infant over the first 3 months of life.D Mothers who had received the treatment scored significantly higher on scales of maternal self-confidence when the child was 4 years old (a difference of 1.3 points in the mean score) and on maternal role satisfaction at age 6 months (a difference of 3.1 points in the mean score).iv The study found no significant differences in maternal anxiety. A 2009 randomized study of 138 Black mothers and their low birthweight, premature infants found that after an 8-session, 20-week Early Intervention program, mothers in the treatment group had significantly higher self-efficacy scores (the mean score was 1.2 points higher on the 40-point Maternal Self-Efficacy scale).H
A 2015 study focused on caregiver-implemented interventions for children with language delays, and although the study found significant impacts on child receptive language (discussed below), there were no significant findings for reducing caregiver stress.E
Optimal Child Health and Development
Cognitive, Motor, and Behavioral Outcomes
Evidence from meta-analyses,A,F,G randomized controlled trials,C,D,E,H and studies using carefully matched comparison groupsB suggests that EI services make a positive difference for the cognitive, motor, and behavioral skills of infants and toddlers with disabilities. For example, a 1987 meta-analysis of 31 studies found an average effect size of 0.62 for the cognitive skills of children in Early Intervention services.F The authors considered this impact to be a “moderate, positive effect” (p. 652)F and they noted some key features of programs that produced the greatest effects: they had more structured curricula, they enrolled children before 6 months old, and they involved parents to a greater degree. For example, services that involved parents and children together produced an average effect size of 0.74, compared to 0.44 for programs that involved either parents or children separately. The effect size for motor skills was somewhat smaller, at 0.43.
A widely cited randomized controlled trial begun in the 1980s, called the Infant Health and Development Program, involved 985 families with infants born low birthweight and premature at eight hospitals across the country.C The infants who were assigned to the EI treatment, which involved intensive services throughout the first 3 years of life, saw better cognitive and behavioral outcomes at age 3 (an average of 9 points higher on the Stanford-Binet Intelligence Quotient test, and an effect size of -0.2 on a behavior problems scale) than the control group, and a greater degree of participation in the program was associated with higher scores on the cognitive assessment. A 2006 follow-up to the study found positive long-term impacts at age 18 on those who had participated in the trial compared to the control group, on both academic and risk behavior assessments.I
The 1988 randomized controlled trial involving infants born low birthweight, discussed in the parental health section above, found that children who received EI services from a nurse showed significantly higher cognitive scores at 36 and 48 months than similar children who did not receive the intervention (a difference of 9.5 points at 36 months and 12.9 points, or approximately 0.8 standard deviations, at 48 months on the McCarthy Scales of Children’s Abilities).D The McCarthy General Cognitive Index, used in this study, has a mean standard score of 100 and a standard deviation of 16 points. The study also found that infants in the experimental group scored better on a scale of infant temperament (the Carey Infant Temperament Questionnaire, in which lower scores reflect more favorable infant temperament) at 6 months old. Low birthweight infants in the EI group scored 1.3 points lower than their counterparts in the control group on the 4-point scale.D
Similarly, a 2012 study using propensity score matching to examine the outcomes of preterm and low birthweight infants found that those who received EI services showed significantly better cognitive development trajectories by 24 and 36 months (using the Bayley Scales of Infant Development at 16 months and the Stanford-Binet scales at 24 and 36 months) than those who did not receive services.B The study also found that among children who received EI services, those whose mothers reported higher levels of maternal support (an index of emotional, financial, respite, and other supports offered by the mother’s family and social networks) saw greater cognitive outcomes relative to the control group. This finding underscores that children’s developmental trajectories are closely tied to their caregivers’ wellbeing.
The 2009 randomized intervention with 138 Black infants born low birthweight and premature found that the extremely low birthweight infants (less than 1,000 grams) assigned to the Early Intervention group scored 10 points higher on the Bayley Mental Development Index (a scale with a mean of 100 and standard deviation of 15) than those infants assigned to the control group.H The study did not find significant effects for infants born weighing more than 1,000 grams.
A 1998 meta-analysis of studies that employed a “randomized, prospective, longitudinal design with appropriate control groups” (p. 321) found effect sizes for cognitive outcomes that ranged from 0.50 to 0.75, depending on the characteristics of the samples examined.G Finally, a 2009 meta-analysis of 25 randomized controlled trials that analyzed various Early Intervention programs for preterm infants found significant differences between the cognitive scores of treatment participants as compared to control groups (a weighted mean difference of 9.7 points at 36 months for studies using the McCarthy and Stanford-Binet scales).A However, differences that were measured at 36 months were no longer detected at 5 years.A
Language and Communication Skills
Studies with rigorous methods have also shown positive impacts of EI services on infants’ and toddlers’ communication skills. In fact, the 1987 meta-analysis discussed above found the greatest effect size for language skills, at 1.17.F A 2015 randomized controlled trial examined the effects of a caregiver-led communication intervention on toddlers facing language delays, and the authors found that the treatment produced significant positive effects on receptive, but not expressive, language skills (a 0.27 to 0.35 effect size for receptive language skills, depending on the instrument used).E
- An impact is considered statistically significant if p<0.05.
- Studies I and J are longer-term analyses for Study C and are not included in Table 2.
- Maternal self-confidence was measured using the Seashore Self-Confidence Rating Paired Comparison Questionnaire, in which a total score is measured by counting the “number of items on which the mother rates herself at least as competent as…five other potential caretakers (spouse, own mother, another experienced mother, a pediatric nurse, and a physician)” (p. 548).D Maternal role satisfaction was measured using a semistructured interview when the infant was 6 months old, and two independent raters used 4-point Likert scales to score the interviews on 10 questions.D