By Susanna Loeb
Early childhood education in the United States is tangle of options—varying in quality, price, structure, and a range of other dimensions. In part as a result, children start kindergarten having had very different experiences in care and very different opportunities to develop the skills and dispositions that will serve them well during school. Systematic differences across groups by income, race, ethnicity, home language, and geographic location are particularly troubling because inequalities that appear early are often sustained through school and affect prospects throughout life.
Convincing research has demonstrated that high-quality early childhood programs can reduce these differences across groups.  A few small programs have demonstrated strong positive effects throughout the life cycle, but even some large-scale programs, such as those in Boston and Tulsa have shown effects on math and reading learning.  These positive results combined with evident need have led to substantial public investment in early childhood education. State spending on preschool more than doubled between 2002 and 2016, from $3.3 to $7.4 billion (constant 2017 dollars). 
Source: Accountability for Early Education — A Different Approach and Some Positive Signs – Education Next : Education Next