"I came near forgetting to tell you about our demerit or "black marks" they give a man one of these "black marks" for almost nothing and if he gets 200 a year they dismiss him. To show how easy one can get these, a man by the name of Grant of this state got eight of these "marks" for not going to Church to day. he was also put under arrest, so he cannot leave his room perhaps fer a month, all this fer not going to Church. We are not only obliged to go to church but must march there by companys. this is not exactly republican." - Cadet US Grant Sept. 22, 1839
"Demerits were handed out for so many reasons that a study in 1914 determined there were 18,000 different opportunities for a cadet to earn a demerit in his four years at West Point. Discipline was so harsh that when West Point undergraduate Ulysses S. Grant learned Congress was considering abolishing West Point as a waste of taxpayer money, he read the newspapers every day looking for news that the legislation had passed. It didn’t, but Grant did, graduating from West Point in 1843....And as more years passed, West Point modernized... And demerits aren’t handed out as liberally, meaning it is possible to graduate today without earning a demerit, something that would have astonished Ulysses S. Grant,
who earned 290 in his four years, or WW I commanding general, John Pershing, who earned 200. It may even have surprised General Robert E. Lee, although he actually did graduate from West Point — in 1829 — without receiving a single demerit." -
SOURCE
The 180 year old West Point log books still surprisingly exist as seen in
THIS REPORT by the New York Historical Society.
It seems that tardiness and improper dress/appearance/equipment were some of Grant's main offenses, but as Grant himself states the marks were given out pretty liberally.