The Harry Potter films are incredibly popular. They are also incredibly criticized for leaving a whole lot out from the source material.
That's not to say that they are bad films. And it's certainly understandable as to why they needed to cut so much from the novels. Virtually every book-to-movie adaptation is forced to cut material, and when it comes to Harry Potter, the producers and writers were forced to condense hundreds of pages' worth of material into two and a half hours' worth of story. It's a tough job.
A lot was lost in the process. Including students. These are five students we never got to see in the movies, and five we didn't really care about.
Never Saw: Terry Boot
Terry Boot has a prominent role in Order of the Phoenix as a member of Dumbledore's Army. Terry directly mentioned that Harry had slain the Basilisk with the Sword of Gryffindor. He also mentions to Hermione that she could have been a Ravenclaw due to her intelligence, and he even helps Harry fight Draco, Crabbe, and Goyle on the Hogwarts Express. He later gives Harry some info regarding Ravenclaw's lost diadem - a role that was given to Cho Chang in the film.
Didn't Care About: Graham Montague
Montague played a small role in the films. He is primarily known as Captain of the Slytherin Quidditch team. In one particular match, Montague incurred a penalty from Madam Hooch after he grabbed Katie Ball's head. He later joined the Inquisitorial Squad under Umbridge, which was meant to root out the location of Dumbledore's Army and ensure Umbridge's rules over Hogwarts. Another slimy Slytherin is not what the movies needed. Apparently he is actually in the movie, but book readers certainly wouldn't know it was him...
Never Saw: Dennis Creevey
The films do the Creevey brothers dirty. Dennis's older brother Colin is given short shrift, only appearing briefly in Chamber of Secrets. And even it's primarily as a plot device, not as a character. Like his older brother, Dennis is a member of Dumbledore's Army, and like Dennis, he was pulled from Hogwarts by his parents following the murder of Dumbledore and ascension of Headmaster Snape. Colin was later killed in the Battle of Hogwarts.
Didn't Care About: Penelope Clearwater
Penelope Clearwater is primarily known as the girlfriend of Percy Weasley. She was directly approached by Harry and Ron while they were disguised as Crabbe and Goyle in order to ascertain the location of the Slytherin common room.
She also joins Hermione on her Basilisk adventure throughout Chamber of Secrets. She, along with Hermione, end up petrified by the Basilisk. None of this is really needed for the films, especially considering Percy's greatly reduced role.
Never Saw: Ernest 'Ernie' Macmillan
Macmillan's face is briefly seen in both Chamber of Secrets and Goblet of Fire, although even book readers may not know it. He is so inconsequential in the films that he may never have been shown at all. This is a shame, because Ernie plays quite a large role in the novels. He has a hesitant if respectful relationship with Harry. They often fight, such as when he accused Harry of being the Heir of Slytherin and when his name emerged from the Goblet of Fire, but he always remained loyal and even joined Dumbledore's Army.
Didn't Care About: Melinda Bobbin
It's great that J.K. Rowling looks to expand her world with numerous names and figures. But oftentimes this results in a slew of names that are just as quickly forgotten. Such is certainly the case with Melinda Bobbin. Bobbin is a member of Slughorn's Slug Club. Her family reportedly owns a large chain of apothecaries, which is why Slughorn wanted her in his exclusive club.
Never Saw: Anthony Goldstein
Goldstein is another prominent member of Dumbledore's Army that the films completely bypassed.
Goldstein was a friend of Terry Boot and was also acquainted with Ernie Macmillan. He was one of Ravenclaw's prefects alongside Padma Patil, and he fought alongside Harry and Terry during the Hogwarts Express fight with Malfoy and his goons. Like the other members of DA, Goldstein fought in the Battle of Hogwarts.
Didn't Care About: Cassius Warrington
Warrington suffers a similar fate to Graham Montague. He reportedly can be seen in Order of the Phoenix, but as nothing more than a background extra. He too is on the Slytherin Quidditch team, serving as chaser. He also reportedly put his name in the Goblet of Fire, and he too served on Umbridge's Inquisitorial Squad. He even managed to catch both Ginny and Neville. Again, none of this is really needed.
Never Saw: Marietta Edgecombe
Edgecombe is another member of Dumbledore's Army, albeit in a very different capacity. Edgecombe was quite prominent throughout Order of the Phoenix, as she is good friends with Cho Chang. However, she eventually betrays Dumbledore's Army to Umbridge after fearing that her participation in the clandestine group would put her mother's job at risk. This role is given to Cho Chang in the Order of the Phoenix film adaptation.
Didn't Care About: Lucian Bole
Bole is another Slytherin Quidditch player no one really cares about. He plays the role of beater, and he once got into a skirmish with George after he clubbed Gryffindor's chaser, Alicia Spinnet. He and his fellow beater, Peregrine Derrick, were replaced by Crabbe and Goyle. It's hard to care about Bole's exclusion from the films, even though George elbowing him in the face was quite satisfying to read.