We are given the exact number in Season 4’s “Mrs. Puff, You’re Fired,” in which SpongeBob’s beloved drivers’ ed teacher Mrs. Puff is grilled by her superintendent Mr. Fitz. Mrs. Puff is informed that she cannot have her teaching certificate renewed to the large number of failing students in her class. When she responds that only SpongeBob has ever failed her boat-driving test, Fitz reminds Mrs. Puff that the number of failures SpongeBob has racked up totals 1,258,056. Whoa.
Though Mrs. Puff is indeed fired for her failure to teach SpongeBob, it doesn’t take her replacement Sergeant Roderick — or Mr. Fitz — that long to realize that Mrs. Puff isn’t the problem. Rather, it is that SpongeBob is unteachable. No matter how many times he fails, he always returns to Mrs. Puff’s class with the same wide-eyed optimism and determination. At least until his anxiety gets the best of him at the beginning of every test. In the end, Mrs. Puff is rehired at the boating school. Unfortunately, this means she will have to keep teaching SpongeBob.