Burris Ewell has head lice in his hair. The lice are just a small part of his filthiness; he shows up for the first day of school as "the filthiest human I had ever seen," and represents, for Miss Caroline, an education of sorts about the realities of teaching school. Her distress at seeing a louse crawl out of Ewell’s hair is only amplified by Ewell’s disdain for her advice to "wash his hair with lye soap" and for the idea of education in general ("Been comin' to the first day o' the first grade fer three year now," he explains). For Burris, lice are just another fact of life, but once he sees Miss Caroline's reaction, he clearly thinks of them as a kind of badge of honor. One of the perks of being a Ewell is a kind of unofficial exemption from attending school; he is asserting this privilege (and his personal power) when he says defiantly as he leaves,

Report and be damned to ye! Ain’t no snot-nosed slut of a schoolteacher ever born c'n make me do nothin'! You ain't makin' me go nowhere, missus. You just remember that, you ain't makin' me go nowhere!

At school, Burris Ewell has cooties (head lice) crawling through his hair.  Burris will not appear throughout the school year, but he does make an appearance at the start of each new school year, in compliance with the truancy officer.

 Burris's appearance, as well as his foul mouth, confound Miss Caroline Fisher, his new teacher.  Scout attempts to acclimate Miss Caroline to her new teaching environment by giving her the lowdown on the Ewell clan, as well as on some of the other families represented within the school.  In her explanation of the families, we get an early introduction to the Ewells as well.  Burris's father, Bob, and his sister, Mayella, factor heavily into the later action of the book, so the early introduction proves helpful.