 CTW solicited the Educational Testing Service ( ETS ) to conduct its summative research . CTW and ETS hired and trained coordinators , testers , and observers from local communities to conduct these studies . The most relevant tests of the show 's effectiveness were comparisons between children who watched it regularly and those who did not . After the first season , however , Sesame Street was so widely watched that it was difficult to make this distinction ; ETS began to have problems finding subjects for their non @-@ viewing groups , which weakened the experimental design . It solved this problem by selecting control @-@ group households from areas that did not broadcast the show . Instead of using groups of viewers and non @-@ viewers , later large @-@ scale studies used statistical designs and methods for estimating cause @-@ effect relationships . 
