A study on upward mobility found good results for King and Snohomish Counties. Every year a kid lives in Snohomish County adds .72% to his earnings at age 26. That is a small number, but, since it is per year, it adds up for a kid raised there from birth to age 20. It means an added $3740 per year over the national average - per year! The numbers for King County are .57% and $2960. That puts them at #2 and #7 of 100 urban counties.
On the other end of the scale Baltimore (an independent city which is treated as a county) the kid has a loss every year; he loses .86% per year growing up for a loss of $4510 per year at age 26 as a result of growing up there. That is very sad.
Washington Research Council reporting on a study by Raj Chetty and Nathaniel Hendren at Harvard.
Update: I added words to emphasize that both the growth and income gains are per year.