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92 as it might not be practical to find or create a list of participants from which random assignments can be made . Figure 1: Pretest-Posttest Control-Group Design 2. Posttest-Only Control-Group Design The Posttest-Only Control-Group Design is also the type of experimental design in which two groups are equivalent because they are randomly assigned. There are no pre-tests done since this design attempts to address testing effects associated with pre-testing by testing only after the experimental group receives the intervention or programme. This is because the process of random assignment provides for equivalence between the experimental and control groups before exposure to the intervention or programme (Rubin & Babbie, 2013). Random Assignment Pre-test Experimental group Post-test Pre-test Control group Post-test Focus Box 5: Pretest-Posttest Control-Group Design A team of researchers evaluated an intervention programme that was aimed at increasing the responsiveness of social workers to the educational needs of foster children through a specialised training and representation from the school to be present at the welfare agencies. 200 social workers who were divided into pilot and control group participated in the study by completing a questionnaire which tested their knowledge of the school system before and after the programme. In addition, document review was done on 300 case files. The findings revealed that the pilot group performed better than the control group, showing a significant increase in knowledge and awareness of the educational and school system among the social workers (Zetlin et al., 2005).