It's well established, just google it. For example:

> Compared with many European countries, for example, few Americans end up with an income or educational level that is substantially different than their parents.

> Now, new research suggests that social mobility in America may be even more limited than researchers have realized.

https://www.washingtonpost.com/news/wonk/wp/2016/10/06/strik...

> US social mobility gap continues to widen

https://www.ft.com/content/7de9165e-c3d2-11e6-9bca-2b93a6856... (Paywall!)

EDIT to add:

> You're twice as likely to live the American Dream in Canada

https://www.businessinsider.com/the-american-dream-of-social...