The general location setting of the books is New York. Holling never actually says that his school is in New York. It's up to the reader to figure it out, but a reader can get that information within the first page of text. Holling is telling his readers about how to get a teacher to hate you, and he says that doing number 400 and 410 would likely get you thrown in prison.
"There were the kinds of things that sent kids to juvenile detention homes in upstate New York, . . ."
If the book was set in California, Holling might have said something about Alcatraz, since it was still likely open when the book is taking place.
Specific setting locations change throughout the novel. Most of the book takes place at Camillo Junior High School. More specific than that is Mrs. Baker's classroom. Another setting is Holling's home. Holling sarcastically refers to it as "The Perfect House." He does that because his home life is definitely not perfect. He also does it because his father once claimed that it is perfectly located to be in the middle of everything.
"Which my father had figured out was right smack in the middle of town. Not on the north side. Not on the south side. Just somewhere in between. 'It's the Perfect House,' he said."
The time period that the novel takes place in is one school year. The book begins in September and ends in June. Each month functions as the chapter title and can't be missed. No specific year is mentioned in the text, but the reader knows that the book is taking place during the Vietnam war. The first indication of that time period is in chapter 1. Holling tells his readers that his family would frequently watch Walter Cronkite give updates and casualty reports on the Vietnam war. Mrs. Baker's husband is also serving in Vietnam and her concern and stress over husband is a frequent element of the story.