1. Abt Associates Inc. (1997, April). Prospects: Student outcomes (final report). Washington, DC: U.S. Department of Education, Planning and Evaluation Service, Office of the Under Secretary.
2. Administration for Children and Families, U.S. Department of Health and Human Services. (2001, February 20). Head Start Legis./Regs./Policies. http://www2.acf.dhhs.gov/programs/hsb/regs/regs/rg_index.htm.
3. Guralnick, M. J. (1997). The effectiveness of early intervention. Baltimore, MD: Brookes.
4. Muthén, B. (2001). Second-generation structural equation modeling with a combination of categorical and continuous latent variables: New opportunities for latent class/latent growth modeling. In L. M. Collins & A. Sayer (Eds.), New methods for the analysis of change (pp. 291–322). Washington, DC: American Psychological Association.
5. Muthén, B., Brown, C. H., Khoo, S., Yang, C., & Jo, B. (1997). General growth mixture modeling of latent trajectory classes: Perspectives and prospects. An earlier version of this paper was presented at the Prevention Science and Methodology Group meeting in Tempe, AZ (1996, May 22–24).