Although the film is set in late 1951 and 1952, Jacy's parents own a 1954 Cadillac convertible.
Just before Jacy goes off with Lester to the pool party, she and Duane are making out in the car. She moves her legs across the seat of the car and is clearly wearing light colored, flat soled shoes with bows on the top. When she takes her shoes off at the pool party, she is wearing shoes with no bows.
The scene where Jacy and Bobby meet in the kitchen during the pool party is wildly out of sync with the chronology of the story, seeming to be cut into the film weeks after the event. Plot-wise it should come just after Sam bans the boys from his establishments, and Sonny's first tryst with Ruth at her home.
When Sonny and Jacy are driving to Oklahoma to get married, several things about Sonny (position, hair, etc) change between shots.
The Texaco sign is missing the letter "E" on one side and "A" on the other; as both sides are seen, some people got confused.
In the opening scene, the "wind" is blowing from the right side of the screen. As the camera pans to the left and Sonny's truck comes into view, a tumbleweed starts to roll from the left into the wind.
When the movie came out, several of the actors (Timothy Bottoms, Cybill Shepherd and Randy Quaid, for example) playing high school teens were in their twenties, far too old to still be in high school. Unless education in Texas was very slow in that era.
When Lois Farrow makes a telephone call from her home she dials a seven digit number. In 1951 a telephone number would have been at the most five digits in the small town of Anarene, Texas.
When Sonny and Jacy are driving to Oklahoma to get married, the highway markings are incorrect. In 1952, Texas highways were marked with a solid line down the middle of the highway with no-passing zones marked with dashed lines.
When the boys are running in the high school gym, the basketball court has a 6 foot lane. In 1951 the lane would have been only 3 feet wide.
Several scenes show television programming, however TV was not introduced to the Wichita Falls area (and Anarene) until 1953. The movie takes place in 1951-52.
When Sonny, Duane, and Jacy leave the high school in her car there is a 1960s car in the driveway of a house.
At the very beginning of the film, Sonny is having trouble starting the old rusty pickup truck. After getting it running he starts to drive off. The soundtrack has him changing gears, but we still see him with both hands on the steering wheel.
The lavalier mic on Duane's tie is visible during the graduation scene.
A full-length shadow of the camera and crew is visible when Sonny drives up to Ruth's house for the first time.
The camera's shadow can be seen at the bottom of the screen as it tracks a car towards the end of the film.
Although he continues to appear in the rest of the picture, nothing is ever made of who takes responsibility for Sam's son Billy after Sam's death.
When Duane returns to Anarene toward the end of the film, he is on leave from the US Army in the middle of the Korean War, around 1952. His hair is too long to pass Army regulations, which limit the length of a soldier's hair, after he has completed basic training. His hair would be too long even for today's Army. Moreover, Duane has sideburns, which the Army would never have permitted.