Todd Graham is director of debate at Southern Illinois University. His teams have won national championships for three years, and he's been recognized twice as the national debate coach of the year. The opinions expressed in this commentary are solely those of the author.

(CNN) The Republican debate in South Carolina Saturday on night was far below what I'd hoped for as a debate coach, so the grades generally reflected that this time. It's like one of those "group projects" where one person in the group is so poor as to bring everyone else down. Sometimes, nobody gets an A.

I'll begin with the best of the lot.

B-

Marco Rubio: Rubio was generally decent (solid in his discussion of child tax-credits, worse on amnesty and immigration and his record in Florida). He had a poor exchange on immigration with Cruz that somehow ended up with Cruz speaking Spanish. It wasn't Rubio's best debate, but since it wasn't the disaster of his last one, where the (now gone) Chris Christie mocked him for repeating himself, people will probably give him too much credit. B minus seems appropriate.

Todd Graham

C-

Ben Carson: Carson continues with two irritating trends. First, he mentions, in a tired joke or complaint, his speaking time. Enough already. Second, he answers every question asked of him by going back to the last topic, saying how he'd would have loved to answer that one, and giving a generic answer like, "I've got some great ideas" or "please see my policy online."

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C-

Jeb Bush: In his first exchange, of many, with Trump, Bush stuttered and stammered even when not provoked. I've seen it in many debates. You expect your opponent's next argument, which causes you to lose your train of thought because you're thinking ahead. With Bush, of course, after that, the inevitable happened. He got into many unwieldy and unprofessional arguments with Trump. Bush's new approach was to attempt humor now and then. Note to Bush: If you aren't a funny guy, then don't try it out in a debate. It backfires almost every time.

C-

John Kasich: He tried to have it both ways. At times, he would pretend that he was above the rest of the raucous field with his calm demeanor (by telling us he was), but then, when he was engaged with Bush, Kasich would revert to interrupting and appearing incensed, as he has in other debating appearances. It has served him poorly.

D

Ted Cruz. Cruz had a decent debate in the middle, but it was bookended by awfulness. Initially, the moderator, John Dickerson, flustered Cruz. At one point, Cruz actually gave Dickerson the stink-eye. No kidding. Google the video. The debate escalated, with Cruz in an argument with Trump, who called Cruz, for the second time that night (Rubio did it earlier) a "liar," and even the "single biggest liar." Cruz's comeback to Trump? "Adults don't interrupt." He's got to find a way to get above this fray. Getting called a liar multiple times in a debate is something to avoid.

F

Donald Trump: He's back to childish again. Trump can't let any criticism go by. His thin-skinned approach ruins the debates and doesn't help him. This is amateur debating. Trump--and I'm not exaggerating--lost his cool every time his name was mentioned in a negative light. His response was invariably to call people names. He constantly interrupted other candidates in mid-speech.

JUST WATCHED Voters ask Donald Trump to 'cut out profanity' Replay More Videos ... MUST WATCH Voters ask Donald Trump to 'cut out profanity' 00:44

Losing your cool at the drop of a hat is poor form in debates. And it's worse for a President. Indeed when asked whether he can ever be told he's wrong, his reply was to spin it into an attack on Bush and how much money he spent in New Hampshire, only to place fourth as opposed to Trump, who won there. Not answering the questions, name-calling, interrupting...all earned Donald Trump an F.

F

The live audience: Enough already! They're annoying; they're biased toward some candidates (they'd cheer at anything Rubio said, regardless of the merit); and biased against others (stop booing Trump and Cruz just because they disagree with your favorite son, Rubio). It's an age-old debating trick: Stack the audience, and watch how they sway the voters (especially the voters at home). At the end it became a contest on whose supporters could yelp the loudest. What nonsense.

F-

The debate: I wrote the words "this is a terrible debate" no less than 5 times in all caps when watching.

The moderators had no control. A good moderator should study the candidates, know their debating style, and prepare to handle it. Most of the candidates — not just Trump -- lacked self-control. If you have kids, here's my analogy. It was like watching children screaming, interrupting, and insulting one another when fighting over that last scoop of ice cream.

As an example of how out-of-control the debate became, Dickerson asked Rubio to "chime in" and Rubio replied, "on anything I want?" So he did.

It ended with another episode when Rubio asked if he had 30 seconds , and Dickerson simply gave up by saying, "I'll ask the question, you do what you want."

It was a perfect summation of a pitiful debate.