At A Glance

Noteworthy Characteristics

  • Measured children’s height and weight.
  • Provides data on food consumption in and out of school, including information on diet reported by the children themselves in later rounds of data collection.
  • Includes measures of physical activity in and outside of school.
  • Includes reports of children’s health and disability.



To collect data on children’s early school experiences from kindergarten through middle school in the United States (U.S.).

Target Population

The kindergarten class of 1998-1999 as they progressed through the 2006-2007 school year (when most were in eighth grade).


Began in 1998. Conducted periodically. Last year of collection was 2007.


National Center for Education Statistics, U.S. Department of Education. Learn more about the federal agencies that collaborated with NCES on the ECLS-K.

Special Note(s)

The Early Childhood Longitudinal Study (ECLS) program includes three longitudinal surveys that examine child development, school readiness, and early school experiences. In addition to the ECLS-K, the ECLS program includes the Early Childhood Longitudinal Study, Birth Cohort (ECLS-B) and the Early Childhood Longitudinal Study, Kindergarten Class of 2010-11 (ECLS-K:2011)

The 1998-1999 ECLS-K base year kindergarten data also represent kindergarten teachers and schools with kindergarten programs in 1998-1999. Additionally, the data collected in 1999-2000 are representative of first graders in that school year.

The Early Childhood Longitudinal Study, Kindergarten Class of 1998-1999 data were collected two times when the children were in kindergarten (1998-1999) and in first grade (1999-2000), and once during the third grade (2002), fifth grade (2004), and eighth grade (2007) school years.

The longitudinal nature of the ECLS-K data enables researchers to study how a wide range of family, school, community, and individual factors are associated with school performance.

System Contact:
Chris Chapman
National Center for Education Statistics
Phone: +1 (202) 245-7103


Sample Design

Longitudinal, multistage probability sample design to obtain a nationally representative sample of children in kindergarten in the United States in 1998-1999. Asians and Pacific Islanders were oversampled, as were children attending private school. To learn more about the ECLS-K sampling design, see the ECLS-K user’s manuals and the ECLS-K website’s Frequently Asked Questions.

Sample Size

Approximately 22,700 children were sampled from 1,300 schools in the 1998-1999 school year. On average, 23 kindergartners were sampled from each ECLS-K school. In some smaller schools, the entire population of kindergarten children was selected.

In the spring of first grade, children who were not in kindergarten in the U.S. during the 1998-1999 school year (i.e., immigrants to the U.S. who arrived after the first 1998 sampling, children living abroad during the 1998-99 school year, children who were in first grade in 1998-1999 and repeated it in 1999-2000, and children who did not attend kindergarten), and therefore did not have a chance to be selected to participate in the base year of the ECLS-K, were added to the first grade sample. Their addition is referred to as “freshening” the sample.

Special Note(s)

The base-year school sample is nationally representative of schools with kindergarten programs. A separate school-level data file with school-level weights is available.

Also during the kindergarten year, the ECLS-K sampled all kindergarten teachers in each of the ECLS-K schools. Data from this nationally representative sample of kindergarten teachers are available as a separate file with teacher-level weights. The ECLS-K data do not support teacher-level or school-level estimates in any year other than the base year.

ECLS-K used a three-stage sample selection process:
• Stage 1: Primary sampling units (PSUs), which were geographic areas consisting of counties or groups of counties.
• Stage 2: Schools within sampled PSUs.
• Stage 3: Children within schools.

Key Variables


NameMethods of Assessment
Child’s birth weightInterview/questionnaire (parent/caregiver)
Child’s date of birthInterview/questionnaire (parent/caregiver)
Child’s race/ethnicityInterview/questionnaire (parent/caregiver)
Child’s sexInterview/questionnaire (parent/caregiver)
Household incomeInterview/questionnaire (parent/caregiver)
Disability (cognitive; equipment use; general; hearing; movement/physical; vision)Interview/questionnaire (multiple sources)


NameMethods of Assessment
Consumption of fruits, vegetables, soda, milk, juices, foods of minimal nutritional value, for all meals consumed during the past 7 days (5th and 8th graders)Interview/questionnaire (child)
Family (child and adult) food security statusInterview/questionnaire (parent/caregiver)
Participation in national school meal programsInterview/questionnaire (parent/school administrator)
Participation in nutrition assistance programsInterview/questionnaire (parent/caregiver)
Percent students in school eligible for free and reduced-price lunchesInterview/questionnaire (school administrator)
Types of food available at schoolInterview/questionnaire (child; school administrator)
Whether family eats breakfast and dinner togetherInterview/questionnaire (parent/caregiver)

Physical Activity-Related

NameMethods of Assessment
Frequency of physical activity each weekInterview/questionnaire (parent/caregiver and child)
Hours spent in sedentary activity (i.e., television viewing, non-school reading, video games, Internet)Interview/questionnaire (parent/caregiver)
Participation in physical education (8th grade only)Interview/questionnaire (child)
Participation in school sportsInterview/questionnaire (child)
Frequency of recess in schoolInterview/questionnaire (teacher)
Participation in extracurricular activitiesInterview/questionnaire (parent/caregiver)


NameMethods of Assessment
Schedule-related sleep environment: Caregiver work scheduleInterview/Questionnaire with Parent
Sleep disturbances and quality: Subjective satisfactionInterview/Questionnaire with Parent
Sleep timing and regularity: Sleep timing on workdays/schooldaysInterview/Questionnaire with Parent


NameMethods of Assessment
Parent/caregiver has concerns about child’s weight or concerns about the child having an eating disorder (8th grade round only)Interview/questionnaire (parent/caregiver)
Child’s attempts to lose weight (8th grade round only)Interview/questionnaire (child)
Characterization of child's weight (e.g., overweight, slightly overweight) (8th grade round only)Interview/questionnaire (child)
Height and weightMeasured


NameMethods of Assessment
Zip code, county and state of child’s household, National Center for Education Statistics school identifier, school’s zip code, county, and stateObtained from sampling frame and field staff records


NameMethods of Assessment
Child health care, visits to doctors and dentists, diagnosesInterview/questionnaire (parent/caregiver)
Parental depressionInterview/questionnaire (parent/caregiver)
Percent minority students in schoolInterview/questionnaire (school administrator)

Data Access and Cost

Data Availability

The most recent data release, the Early Childhood Longitudinal Study, Kindergarten Class of 1998-99 (ECLS-K) Kindergarten Through Eighth Grade Full Sample Public-Use Data and Documentation is available online. It also is available on a DVD that includes the data files, electronic codebooks (ECBs), user’s manuals, survey instruments, and file record layouts. Learn more about how to obtain the DVD.


Free of charge.

Special Note(s)

Both restricted-use and public-use data files are available. Learn more about the difference between restricted-use and public-use data files. A restricted data license must be obtained before users can access the DVD containing restricted-use files. Learn more about how to obtain a restricted data license.


Geocode Variable(s)

Census tract and zip code tabulation area (ZCTA) codes for ECLS-K children's homes and schools are available for each round of the ECLS-K up to third grade. These data are available on the “Census Data and Geocoded Location for the Early Childhood Longitudinal Study, Kindergarten Class of 1998-99 (ECLS-K)” supplemental restricted-use file DVD, available to restricted-use license holders upon request to the Institute of Education Sciences (IES) Data Security Office. This file also has about 600 census variables (or census-derived variables) for each census tract and ZCTA, including income, race/ethnicity, and many other sociodemographic characteristics. Supporting documentation is included on the DVD and consists of a user’s manual, data file record layouts describing the variables on each of the ASCII data files, and code for converting the data files.

Home zip codes, school zip codes, and school Federal Information Processing Standard (FIPS) codes (both state and county) also are available for fifth and eighth grades. Additional information, including home FIPS codes and tract and block data, is available for eighth grade. The fifth- and eighth-grade restricted-use geocode data are available by request from the IES Data Security Office as individual password-protected files for each round.

The restricted-use files have a variable RxFIPSST that indicates the state's FIPS code (the "x" refers to the round number).

Existing Linkages

Additional information on children’s schools is available by linking to school data from the National Center for Educational Statistics Common Core of Data (NCES/CCD) and Private School Universe Survey/Private School Survey Series (PSS) universe files, which pertain to U.S. public and private schools, respectively.

Special Note(s)

An IES Restricted-Use Data License is required to obtain geocode variables.

Although the restricted data do identify children’s state of residence, the ECLS-K sample was not designed to support state-level (or city- or county-level) estimates, as the sample is not representative of children in particular states (or cities or counties).

Selected Publications

For additional publications using ECLS-K data, visit ECLS Publications and Products and ECLS Bibliography.


Fernandez MM. The effect of soft drink availability in elementary schools on consumption. Journal of the American Dietetic Association 2008;108(9):1445-1452.

Jyoti D, Frongillo E, Jones S. Food insecurity affects school children’s academic performance, weight gain and social skills. The Journal of Nutrition 2005;135(12):2831-2839.

Oza-Frank R, Zavodny M, and Cunningham S. Beverage Displacement Between Elementary and Middle School, 2004-2007. Journal of the Academy of Nutrition & Dietetics, 2012; 112(9): 1390-1396.

Taber, D., Chriqui, J, Perna, F., Powell, L., and Chaloupka, F. Weight Status Among Adolescents in States that Govern Competitive Food Nutrition Content. Pediatrics, 2012; 130(3): 437-444.

Physical Activity-Related

Beets MW, Foley JT. Association of father involvement and neighborhood quality to kindergarteners’ physical activity: A multilevel structural equation model. American Journal of Health Promotion 2008;22(3):195-203.

Brewer M, Kimbro RT. Neighborhood context and immigrant children's physical activity. Soc Sci Med. 2014 Sep;116:1-9.

Stevens TA, To Y, Stevenson SJ, Lochbaum MR. The Importance of Physical Activity and Physical Education in the Prediction of Academic Achievement. Journal of Sport Behavior, 2008; 31(4): 368-388.


Datar A, Sturm R. Physical education in elementary school and body mass index: Evidence from the Early Childhood Longitudinal Study. American Journal of Public Health 2004;94(9):1501-1506.

Gable S, Chang Y, Krull J. Television watching and frequency of family meals are predictive of overweight onset and persistence in a national sample of school-aged children. Journal of the American Dietetic Association 2007;107(1):53-61.

Gable S, Krull J, Chang Y. Boys’ and Girls’ Weight Status and Math Performance from Kindergarten Entry Through Fifth Grade: A Mediated Analysis. Child Development 2012; 83(5): 1822-1839.

Kenney EL, Gortmaker SL, Davison KK, Austin SB. The academic penalty for gaining weight: a longitudinal, change-in-change analysis of BMI and perceived academic ability in middle school students. Int J Obes (Lond). 2015 May 18.

Sturm R, Datar A. Body mass index in elementary school children, metropolitan area food prices and food outlet density. Public Health 2005;119(12):1059-1068.

Sturm R, Powell LM, Chriqui JF, Chaloupka FJ. Soda taxes, soft drink consumption, and children’s body mass index. Health Affairs 2010;29(5):1052-1058.

Taber DR, Chriqui JF, Perna FM, Powell LM, Caloupka FJ. Weight status among adolescents in states that govern competitive food nutrition content. Pediatrics 2012; 130(3):437-444

Yiting C, and Gable S. Predicting Weight Status Stability and Change from Fifth Grade to Eighth Grade: The Significant Role of Adolescents’ Social-Emotional Well-Being. Journal of Adolescent Health 2012.


Najarian M, Pollack JM, Sorongon AG. Early Childhood Longitudinal Study, Kindergarten Class of 1998–99 (ECLS-K), psychometric report for the eighth grade. Washington (DC): National Center for Education Statistics, Institute of Education Sciences, U.S. Department of Education, 2009. NCES 2009–002.

Tourangeau K, Lê T, Nord C, Sorongon AG. Early Childhood Longitudinal Study, Kindergarten Class of 1998–99 (ECLS-K), eighth-grade methodology report. Washington (DC): National Center for Education Statistics, Institute of Education Sciences, U.S. Department of Education, 2009. NCES 2009–003.

Walston J, Rathbun A, Germino Hausken E. (2008). Eighth grade: First findings from the final round of the Early Childhood Longitudinal Study, Kindergarten Class of 1998-99. Washington (DC): National Center for Education Statistics, Institute of Education Sciences, U.S. Department of Education, 2008. NCES 2008-088.



Combined User's Manual for the ECLS-K Eighth-Grade and K-8 Full Sample Data Files and Electronic Codebooks


Before conducting any analyses, users are encouraged to review the ECLS-K study instrumentation to fully understand the study’s content, the flow of the items in the questionnaires/interviews, the group of respondents who answered specific questions, and the context in which the questions were asked.

The ECLS-K direct child assessment batteries are not publicly available due to copyright restrictions.