These are just some of the statistics that I kept in mind while developing the Owning Words for Literacy™ series:

• First-grade children from higher-SES (socio-economic status) groups know about twice as many words as lower SES children (Graves, Brunetti, & Slater, 1982; Graves & Slater, 1987).
  
  
• High school seniors near the top of their class know about four times as many words as their lower-performing classmates (Smith, 1941).
  
  
• High-knowledge third graders have vocabularies about equal to lowest-performing 12th graders (Smith, 1941).

Most chilling however, is the finding that once established, such differences appear difficult to ameliorate (Biemiller, 1999; Hart & Risley, 1995). From Beck, McKeown, & Kucan. (2002). Bringing Words to Life (an outstanding book, by the way!)