Final answer:
The Supreme Court used the 14th Amendment to disallow segregation in the Brown decision by ruling that segregated schools violated the equal protection clause.
The Court considered the impact of segregation on Black children and overturned the previous ruling in Plessy v. Ferguson.
Step-by-step explanation:
In the landmark case of Brown v. Board of Education, the Supreme Court used the 14th Amendment to disallow segregation in public schools.
The Court unanimously ruled that segregated schools violated the equal protection clause of the Amendment. They determined that even if the facilities were equal, the doctrine of 'separate but equal' had a detrimental impact on Black children, causing feelings of inferiority.
This decision overturned the previous ruling in Plessy v. Ferguson, which had upheld segregation.