Flynn also discovered that back in the 1950s, the gap between the vocabulary levels of adults and children, especially teenagers, was much smaller than it is in the early twenty-first century. He asserted that some of the reasons for this are the surge in interest in higher education and cultural changes. The number of Americans pursuing tertiary qualifications and cognitively demanding jobs has risen significantly since the 1950s. This boosted the level of vocabulary among adults. Back in the 1950s, children generally imitated their parents and adopted their vocabulary. This was no longer the case in the 2000s, when teenagers often developed their own subculture and as such were less likely to use adult-level vocabulary on their essays.