Last year in San Mateo, Calif., a history teacher at Hillsdale High School conducted a mock hearing of South Africa’s Truth and Reconciliation Commission. Sophia Heath, then a freshman, played an anti-apartheid lawyer. She recalls that she “was really excited and that was the beginning of where my activism started.” On the web, she found Coalition Z, a youth group that registers voters and presses officials to combat climate change, provide more equitable school funding and enact gun control. Ms. Heath started a local chapter.

Its first activity, after the killing of George Floyd in Minneapolis, was a Black Lives Matter demonstration on June 3 at San Mateo City Hall. Ms. Heath and her Coalition Z chapter members used Instagram to recruit young participants and Nextdoor to recruit adults. Speakers included the mayor, the local congresswoman, a school board member and an N.A.A.C.P. official. The police estimated a crowd of over 2,000. Signs and chants called for an end to systemic racism, including police militarization and brutality. Protesters also called for reparations to compensate African-Americans for centuries of enslavement and oppression.

Nationwide, something like 20 million Americans participated in similar demonstrations. Some won commitments for police reform, and others continue to wage campaigns to achieve it.

Black Lives Matter protests have laid a foundation for real change. But in their aftermath, activists in San Mateo and similar communities mostly lack a continuing program to tackle the comprehensive racial inequality that allows abusive police practices to flourish. Ms. Heath and her recruits, young and grown-up, have untapped opportunities to take action in their own town, contributing to a new civil rights movement for racial progress.

San Mateo is a segregated Silicon Valley city. Ms. Heath observes that there are no Black families in her Hillsdale neighborhood. San Mateo’s few remaining African-Americans mostly live in another neighborhood, where they have long been concentrated. One percent of Hillsdale High School students are Black.

Ms. Heath says she would like to live in a more diverse neighborhood. The way to do that, she says, is to insist that the City Council provide more affordable housing — subsidized units for low-income families — in her neighborhood. That would be a step forward, but most African-Americans are not poor; working- and middle-class Black families whose incomes are too high to qualify for existing subsidies were also excluded from neighborhoods like Hillside because of their race.

Effective strategies to redress segregation in all its forms would become clearer if activists in San Mateo and elsewhere did deep research into how their communities’ racial boundaries were established.