Think of Mr. Lingerle as the guinea pig for the Tillermans' experiments in reaching out.
A lonely, obese music teacher, he gives Maybeth piano lessons and becomes an honorary member of the Tillerman family, sharing Thanksgiving dinner with them and babysitting the younger children when Dicey and Gram go to Boston. By the end of the novel, it's clear that this guy's as good as a member of the family.
To say that the Tillermans are a close-knit family is an understatement, but to everybody’s surprise, they learn that they can adopt another member. Mr. Lingerle’s thrilled, the Tillermans are thrilled, and everybody’s ridiculously uncomfortable:
Mr. Lingerle put down his cup, so fast the china clattered. "I’m sorry, I didn’t realize," he said. He started to push himself up, out of the chair. "I’ve stayed too long, I was just too comfortable, I’d better be going." (5.7)
Really, it’s kind of painful to watch sometimes. But every time he accepts an invitation to dinner, he gets one step closer to being an Honorary Tillerman, and the Tillermans get one step closer to expanding their ranks.
Gram has always hated taking charity, but because Mr. Lingerle’s become like family, she accepts an envelope full of cash from him when she and Dicey go to Boston to bring Liza home. If the entire story of Dicey’s Song could be summed up in one quote, it’s what Gram says to Mr. Lingerle as she takes the envelope: "You don’t go reaching out with your hand closed up" (7.165). Oh man, ain't that the truth? In accepting Mr. Lingerle's help, Gram shows her grandkids that a little help between friends and family is a-okay. And she's also showing Mr. Lingerle how much they value his presence.