Zac Efron's tattoo on his right arm is covered with makeup throughout the film but is visible in the sequence with Irene and Dean at the dinner table.
When Dean and Ben have the roadside fight. Ben drops the hammer nearby the roadside he is working on. They fight further in the cornfield and somehow the hammer is there next to them.
When Dean is driving in the ARCA race at Iowa Speedway, it shows him shifting in his race car. On oval tracks like that, the drivers do not change gears at racing speed, only when entering and exiting the pits.
When Brad is down in the field, although his eyes are closed and is supposed to be dead, his eyes are still moving.
(at around 59 mins) The postcard that Dean receives from his brother in Argentina has a correct Iowa address, but is missing USA in the address line. An international postcard would find its way in the mail from Argentina without the correct country in the address.
The Whipple family lives in Churdan, Iowa. They are shown several times driving past a sign that says "Decatur 12 miles." Both are real towns in Iowa, but are actually about 150 miles apart. Neither is in southwest Iowa, as Zac Efron's character is introduced at the speedway.