Skipped Parts (2000) on Netflix

It's 1963. Poor little rich girl Lydia and her 14-year-old love-child Sam are banished from North Carolina while her powerful father runs for governor. They end up in Wyoming where she parties and Sam finds he's one of only two Grosvant High School students who read. Maurey is the other, a pre-pubescent girl wanting to discover what sex is about. She and Sam set out to learn with help from Lydia, who tells them it stops when Maurey has her first period. Trouble is, pregnancy comes first. In this small town, what can Maurey do, and will Sam have any say? Meantime, Hank Elkrunner, a Blackfoot, falls for the feckless Lydia, while her dictatorial dad keeps tabs on them all from afar.