[5] Welner joined the faculty of the University of Colorado Boulder School of Education in 1999 as an Assistant Professor.

[8] Welner is notable for making technical research documents that are accessible to the general public,[9] and for participating in public academic debates on education reform issues such as standardized testing[10] and school choice.

[4][16] In 2005, Welner conducted research on school vouchers as a resident of the Rockefeller Foundation Bellagio Center.

The book provided an early explanation of the legal and policy issues surrounding a then-new type of private school vouchers.

In Closing the Opportunity Gap: What America Must Do to Give Every Child an Even Chance, Welner examines factors that lead to educational disparities and suggests strategies to address them.