Shortly after Elle is kicked out of Professor Stromwell's class, and meets Emmett, she runs into Warner, and immediately after him, Vivian. This would make no sense, as Stromwell's class had just started and Vivian would still be there.
When the new students are in a circle to introduce themselves there are 6 students shown in the shot of all of them, however when they go round all students individually there are only 5 (including the experienced student) because the fourth student is cut out.
Warner's hair changes from being combed over (left to right) when he picks Elle up at the sorority house to straight back in the restaurant, also shorter. It is again combed over when he picks her up in the car shortly after.
It would be nearly impossible for Brooke Taylor to live in a mansion in the Beacon Hill section of Boston. Mansions found on Beacon Hill do not sit on enough land to have a pool. The area is too densely inhabited.
Characters make casual references to numerical class ranks at both Harvard and Yale Law Schools. Neither law school ranks students in this manner (Harvard has not done so since the late 1960s), and Yale Law School does not even assign grades (classes are pass/fail).
When a witness is testifying in a trial, they are only sworn in once, before they are questioned. If they retake the stand for further questioning, they are reminded of their oath. However, Chutney is sworn in the first time - when she is testifying before her mother and the pool attendant - and then again when she goes to answer questions for Elle.
We know that Elle and Warner are both in Callahan's class together, but that Warner is not in Stromwell's class with Elle. However, Harvard, like most law schools, divides its first year class into sections that take every class together. Warner should either be in all of the same classes as Elle or none of them.
When Elle and Paulette are confronting Paulette's ex-husband about Paulette having custody of their dog, Rufus, Elle says that Paulette has custody rights according to Habeas Corpus. Habeas Corpus allows a prisoner the right to be presented before a court by a bailiff, not the right to have custody of pets. However, Elle is merely using this term so as to sound official and to confuse Paulette's ex-husband, not to be correct in her terminology.
When Elle's friends Serena and Margot deliver the good luck card at the beginning of the movie, Serena licks and seal the envelope, then Margot slides it under Elle's door. When Elle opens it moments later, the glue should still be wet yet she has to rip the open as if the glue was dry.
The goof items below may give away important plot points.
After Elle wins the case, reporters are surrounding her as she and Brooke walk down the stairs. After one reporter asks a question, you can clearly hear Brooke's voice answering the question, however, her lips don't move.
The graduates are all shown wearing identical hoods over their black gowns. In reality, graduates at Harvard Law School Commencement wear a hood with colors that represent the institution of their highest prior degree, which would differ for each individual.
In the final graduation scene, the faculty members on the stage are all wearing mortarboard caps. In fact, they should be wearing the traditional "doctors" graduation caps which resemble Scottish tam-o-shanters.
Brooke could not have hired Elle as her attorney after firing Callahan. Although Massachusetts Supreme Judicial Court rule 3.03 (cited in the film) does state that a law student may appear in court under the supervision of a licensed attorney, two key points from that rule are left out, either of which would have barred Elle from representing Brooke. One, the law student must have taken Evidence, which is not a first year class at Harvard or any other law school. Two, in order to appear in court in a criminal case, the law student must be a third year student.
When Elle gets in the lift after she has been propositioned by her professor in his office (before she takes over in court), before the lift doors close Vivian's reflection can clearly be seen in the brass plaque opposite the lift before she moves into the shot and converses with Elle.