hart and risley (2003) spent 2½ years observing 42 families for an hour each month to learn what typical home life was like for 1- and 2-year-old children. the families were grouped into 4 variables, upper ses, middle ses, lower ses and just a few that were on welfare. the middle- and low-ses families were grouped in the final analysis. they found that by age 3 children in welfare families had a vocabulary of 525 words where children in upper-ses families had vocabulary of 1,116 words. they also found that the children in upper-class families were learning vocabulary at a faster rate. the researchers suggested the reason for this difference is because the welfare children heard on average 616 words per hour where professional-family children heard on average 2,153 words per hour. thus, proposing the 30-million-word gap. the achievement gap is explained as a result of the language gap, in that because children are lacking in their vocabulary and literary skills, they will not be as successful in academics. hart and risley argue this is an indispensable societal concern because it sets the child at a disadvantage for not being exposed to more vocabulary skills at a young age.