Old Man and the C- is the twenty-eighth episode of Season 7.
After failing miserably on a television program called "Are You Brighter Than a 6th Grader?" by answering "Sea Cucumber" to nearly all the questions, Mr. Turner reveals he dropped off school at 5th grade when a kid named Melvin said he was "too cool for school". Fearing that this will possibly rub off on his son, Mrs. Turner forces her husband to go back to school, and Mr. Turner ends up and Mr. Crocker's class with Timmy! At first he works hard to graduate from Dimmsdale Elementary School and make his son proud, but after he meets Melvin (now a janitor) and he tells him he's still "too cool for school", Mr. Turner's attendance starts to slip, and Timmy must convince his father to finish school and make his family proud!.
Timmy's Dad enters the game show "Are You Brighter Than a 6th Grader?" and loses because he answered "sea cucumber" to nearly all of the questions. As the Turners left the set with the consolation prize: a lifetime supply of 'macaroni without cheese'. Mr. Turner reveals he dropped out of school in Grade 5 when a nerdy kid named Melvin told him he was "too cool for school". Timmy asks his father if he could drop out school too, to which Mom refuses and makes Dad return to school. Timmy realizes his father is in his class, as he dropped out in the 5th grade. Crocker sees that there are two Turners and shoots two giant 'metal F's at them with his newly-made 'F' Blaster. Mr. Turner avoids his, because he is set to graduate 5th grade to make Timmy proud. After he gives Crocker a box of macaroni as a gift, this makes Crocker renames Mr. Turner, Turner (the name he used for Timmy) and renames Timmy "Becky". He also becomes the teacher's pet, and he also befriends Elmer, Sanjay and Chester. When the four are going for ice-cream, Melvin (now a janitor) tells him he is still too cool for school, so Dad drops out of school again.
After some time, Mom tells Timmy that Dad will fail the year if he continues skipping school so Timmy goes with Crocker. They set up a deal: Timmy will give Crocker his macaroni boxes, and then Crocker will let Dad do the Big Super Test, which lets the taker pass the year automatically. Timmy tries to convince Dad to take the test, but he thinks the test is too geeky for him. Timmy tells him that he's making the same mistake he did as a kid and told him that he is not proud of what he is doing. Mr. Turner burst into tears and realizes Timmy is right, so he decides to take it to make his son proud. This leads to a Rocky Balboa-esque montage where they study for the test. At the Dimmadome, the host of the game show will host the test. Dad is on a roll, answering all the questions the host asked him and some he didn't even ask him. When Dad is at one question of graduating high school, the final question is: "Which sea vegetable would suit perfectly on an undersea salad?" Timmy tells Dad he trust him and that he knows this from the game show he took, to which Dad shouts "SEA CUCUMBER!" and graduates. To celebrate, Timmy and his father toilet paper their own house. As Melvin approaches their house, saying that they are "too cool for school", they beat him up.