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Study Overview
Since its beginning in 1965 as a part of the War on Poverty, Head Start’s goal has been to boost the school readiness of low-income children. Based on a “whole child” model, the program provides comprehensive services that include preschool education; medical, dental, and mental health care; nutrition services; and efforts to help parents foster their child’s development. Head Start services are designed to be responsive to each child’s and family’s ethnic, cultural, and linguistic heritage.
Study Goals
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In the 1998 reauthorization of Head Start, Congress mandated that the US Department of Health and Human Services (DHHS) determine, on a national level, the impact of Head Start on the children it serves. As noted by the Advisory Committee on Head Start Research, this legislative mandate required that the impact study address two main research questions:4
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“What difference does Head Start make to key outcomes of development and learning (and in particular, the multiple domains of school readiness) for low-income children? What difference does Head Start make to parental practices that contribute to children’s school readiness?”
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“ Under what circumstances does Head Start achieve the greatest impact? What works for which children? What Head Start services are most related to impact? ”
Random Assignment Newly entering 3-and 4-year-old Head Start applicants were randomly assigned either to a treatment group that had access to Head Start services or to a control group that could receive any other non-Head Start services chosen by their parents. |
To reliably answer these questions, a nationally representative sample of Head Start programs and newly entering 3- and 4-year-old children was selected, and children were randomly assigned either to a treatment group that had access to Head Start services or to a control group that could receive any other non-Head Start services available in the community, chosen by their parents. Under this randomized design, a simple comparison of outcomes for the two groups yields an unbiased estimate of the impact of access to Head Start on children’s school readiness. This research design, if properly implemented, ensures that the two groups will not differ in any systematic or unmeasured way except through their access to Head Start services.
In addition to random assignment, this study is set apart from most program evaluations because children were selected at random from those applying for entry into Head Start in a nationally representative sample of programs, making results generalizable to the entire Head Start program, not just to the selected samples of programs and children.
Study Sample The nationally representative study sample, spread over 23 different states, consists of a total of 84 randomly selected grantees/delegate agencies, 383 randomly selected Head Start centers, and a total of 4,667 newly entering children; 2,559 3-year-olds and 2,108 4-year-olds. |
One constraint imposed on this study was that selected Head Start grantees and centers had to have a sufficient number of "extra" applicants for the 2002-03 program year to allow for the creation of a non-Head Start control group through random assignment, thereby avoiding ethical concerns about possible denial of services to eligible children. As a consequence, the study was conducted in communities that had more children eligible for Head Start than could be served with the existing number of funded slots.
At each of the selected Head Start centers, program staff provided information about the study to parents at the time enrollment applications were distributed. Parents were told that enrollment procedures would be different for the 2002-03 Head Start year and that some decisions regarding enrollment would be made using a lottery-like process. Local agency staff implemented their typical process of reviewing enrollment applications and screening children for admission to Head Start based on criteria approved by their respective Policy Councils. No changes were made to these locally established ranking criteria.
Information was collected on all children determined to be eligible for enrollment in fall 2002, and an average sample of 27 children per center was selected from this pool: 16 who were assigned to the Head Start group and 11 who were assigned to the non-Head Start group. Random assignment was done separately for two study samples—newly entering 3-year-olds (to be studied through two years of Head Start participation, kindergarten, and 1st grade) and newly entering 4-year-olds (studied through one year of Head Start participation, kindergarten, and 1st grade).
The total sample, spread over 23 different states, consists of 84 randomly selected Head Start grantees/delegate agencies, 383 randomly selected Head Start centers, and a total of 4,667 newly entering children, including 2,559 in the 3-year-old group and 2,108 in the 4-year-old group.5 No statistically significant differences were found between the children randomly assigned to the Head Start and non-Head Start groups, providing one of several indications that the initial randomization was accomplished with high integrity, necessary for the validity of the impact estimates.
Data Collection
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Data collection began in the fall of 2002 and will continue through the spring of 2006, following children from age of entry into Head Start through the end of 1st grade. Comparable data are being collected for both Head Start and non-Head Start children, including interviews with parents, direct child assessments, surveys of Head Start and non-Head Start teachers, interviews with center directors and other care providers, direct observations of the quality of various care settings, and care provider ratings of children.
To date, response rates have been very good, with 83 percent of parents completing interviews in fall 2002 and spring 2003, and assessments being completed for 82 percent of the children. There is some difference in response rates between the Head Start and non-Head Start groups. Statistical weighting has been used both to adjust for the observed non-response and to generalize the data to the national Head Start program.
Statistical analysis of the characteristics of the sample used in this report (i.e., those children and parents for whom data were collected in spring 2003) indicate that the Head Start and non-Head Start groups are well matched on available characteristics, with only two small differences for each of the two age groups. These differences are not fully accounted for by the use of non-response adjustments to the sampling weights and are instead dealt with through their inclusion as covariates in the statistical models used to estimate program impacts.
Although every effort was made to ensure complete compliance with random assignment, some children accepted into Head Start did not participate in the program (this is not an uncommon occurrence in the program), and some children assigned to the non-Head Start group nevertheless entered the program, typically at centers that were not in the study sample. Statistical procedures for dealing with these events are discussed in the report. The findings in this report provide estimates of both the impact of access to Head Start using the sample of all randomly assigned children and a preliminary look at the impact of Head Start on program participants (adjusting for the deviations from random assignment).
4 Advisory Committee on Head Start Research and Evaluation (1999). Evaluating Head Start: A Recommended Framework for Studying the Impact of the Head Start Program. Washington, DC: US Department of Health and Human Services. (back)
5 The sample of 3-year-olds is slightly larger than the sample of 4-year-olds to protect against the possibility of higher study attrition resulting from an additional year of longitudinal data collection for the younger children. (back)
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