Here's some evidence: Hanushek and Woessmann compare countries and identify tracking effects by comparing differences in outcomes:
The results suggest that early tracking increases educational inequality. While less clear, there is also a tendency for early tracking to reduce mean performance.
This is, by far, not one single study that shows that early tracking reinforces the impact of family background. Just one further example, Giorgio Brunello and Daniele Checchi :
early tracking reinforces the family background effects on the years of completed education, on the probability of dropping out and of enrolling or graduating in college. Therefore, in countries with less pronounced tracking, the difference in the dropout rate and college enrolment or completion between the children of poorly and better educated parents is smaller than in countries with stronger tracking.