Kwanzaa is a spiritual, cultural holiday, but it’s practical, too. The Jacksons, who’ve observed Kwanzaa since the 1970s, almost since its inception, use it to set goals and measure success.“It’s a celebration where people can build a better self, better family, better community,” said Portia Jackson, a staffer at The Children’s Museum.Last year her son Bakari, a student at Fort Valley State University in Georgia, pledged to get involved in the campus radio station. This semester, he was named program director.“I’d say my family is Afro-centric,” Bakari said. “Kwanzaa is just something we’ve always done, to understand where we’ve come from.”Kwanzaa is a newbie as holidays go — even Father’s Day is twice as old — and it’s difficult to calculate Kwanzaa’s reach. A 2004 study by the National Retail Foundation reported that 13 percent of African-Americans observed it.But those findings have been called into question because Kwanzaa is not part of mainstream commerce and so is hard to measure.It involves a gift exchange, but not a Christmas-style spend-o-rama. Kwanzaa gifts are often homemade.“How can they say 13 percent?” says Mmoja Ajabu, a Christian minister. “I would not make a guess, but I’d expect it’d be more than 13 percent.”The holiday has gained traction since Ajabu, a former Black Panther leader, started celebrating it in the mid-1970s.Back then, black churches resisted Kwanzaa, which seemed to compete with Christmas.It doesn’t compete with Christmas, though. It’s not religious (the Jacksons are devout Baptists), and today many black churches embrace Kwanzaa, including Light of the World Christian Church, where Ajabu is minister of social concerns, and Ebenezer Missionary Baptist Church.At Ebenezer, the Rev. Thomas Brown plans to use Kwanzaa as the basis for his Sunday sermon. “I have a traditional Baptist church,” he said, “but I am completely comfortable mixing in the message — the spirit — of what Kwanzaa is all about. You can take the seven principles and tie it in with the seven virtues (of Christianity).”About 300 people are expected at a Kwanzaa celebration today at Coleman Academy.There will be a candle lighting, dancing and drumming, with some of the drumming by Bakari Jackson.