Final answer:
Busing was a successful proactive measure in integrating school districts after segregation was deemed unconstitutional.
Step-by-step explanation:
A proactive measure that was successful at helping to integrate school districts after segregation was deemed unconstitutional was the practice of busing.
This involved transporting students to schools outside their neighborhoods in order to achieve racial diversity and balance.
For example, in the case of Swann v. Charlotte-Mecklenburg Board of Education, the Supreme Court upheld the practice of busing in Charlotte, North Carolina, as a means of achieving racial integration.