Rafaela Espinal held her first poolside chat last summer, offering cheese, crackers and apple cider to draw people to hear her pitch.

She keeps a handful of brochures in her purse, and also gives a few to her daughter before she leaves for school each morning. She painted signs on the windows of her Chrysler minivan, turning it into a mobile advertisement.

It is all an effort to build awareness for her product, which is not new, but is in need of an image makeover: a public school in Harlem.

As charter schools have grown around the country, both in number and in popularity, public school principals like Ms. Espinal are being forced to compete for bodies or risk having their schools closed. So among their many challenges, some of these principals, who had never given much thought to attracting students, have been spending considerable time toiling over ways to market their schools. They are revamping school logos, encouraging students and teachers to wear T-shirts emblazoned with the new designs. They emphasize their after-school programs as an alternative to the extended days at many charter schools. A few have worked with professional marketing firms to create sophisticated Web sites and blogs.