First, we should recognize that the NAACP was much older than the other two organizations. It was founded in the first decade of the twentieth century, whereas the SCLC and SNCC were founded in the midst of the post–World War II struggle for civil rights. Early on, the NAACP adopted a strategy it would pursue throughout the twentieth century. The NAACP lobbied for civil rights legislation, beginning with its crusade for anti-lynching laws in the early twentieth century. It maintained a legal fund and financed lawyers who challenged discriminatory laws in court (for example, NAACP attorneys argued the landmark Brown v. Board of Education case before the Supreme Court in 1954).
The SCLC, or Southern Christian Leadership Conference, was born in the wake of the Montgomery Bus Boycotts, which ended successfully with the full integration of buses in the Alabama capital. The SCLC, centered in African-American churches and headed by Martin Luther King, Jr., was an attempt to expand the struggle that had emerged in Montgomery to the rest of the South. Its focus changed throughout the movement, but its methods and core philosophy never changed. The SCLC remained committed to direct nonviolent action to resist racial injustice. It used its resources and the popularity of King to lead voter registration drives, desegregation campaigns, and, later in the 1960s, to advocate for economic justice, as in the Memphis, Tennessee strike of sanitation workers. It was while visiting in support of these strikes that King was assassinated in April of 1968.
SNCC (pronounced "snick"), the Student Nonviolent Coordinating Committee, had its origins in the sit-in movements of 1960. It formed in 1960 at Shaw University in Raleigh, North Carolina. SNCC was dominated by young activists, and these men and women focused from the early days of the movement on local organization rather than the centralized leadership model of the other two organizations. SNCC "field workers" established local units that sought to build an organic, grass-roots movement. They also tended, from the early 1960s, to be more radical in their demands and less willing to wait on political action at the federal level, a major goal of King and the NAACP. Along with CORE (Congress of Racial Equality), SNCC workers were instrumental in the Mississippi Freedom Summer movement in 1964. (It was CORE, not SNCC, which had organized the Freedom Riders in 1961). By the mid-sixties many in SNCC had become impatient with the pace of change and began to turn away from the message of racial reconciliation so crucial to King's appeal. The figure usually associated with this turn was Stokley Carmichael, whose appeal to "black power" pushed the movement in a new, more radical direction. SNCC expelled its white members and even, despite its name, abandoned nonviolence as an imperative. So SNCC differed from the NAACP and SCLC in many fundamental ways.