Final answer:
The popularity of enrichment classes for young children among the middle class significantly grew during the 1960s, a decade marked by economic prosperity and an increased focus on education as a means of social advancement.
Step-by-step explanation:
Lessons and enrichment classes became much more popular among the middle class during the 1960s. This was a period of significant economic growth and prosperity for the middle class in the United States, leading to an increase in consumer spending, higher standards of living, and a greater focus on education and self-improvement. Public school enrollment soared and higher education became more accessible, with the emerging middle class placing a high value on education as a means to maintain their status. With more disposable income and value placed on self-improvement, middle-class parents increasingly invested in their children's future through various enrichment opportunities.