Mistakes and goofs and continuity errors in the series:
In the episode Pilot the seating plan in Ms. Mayhew's class (English) changes during the scene and some people disappear.
In the episode The Substitute Patty claims that they do not have a basement. However, in Life of Brian Patty says, "I can't do braids in a basement" and Graham gets the wallpaper from the basement. In the scene when Patty and Graham are talking in the kitchen, right after Principal Foster's reveals the truth about Vic, the boom mic is clearly visible.
In the episode Strangers in the House when Patty fires Graham, he is wearing a tee shirt. When he goes to hug Patty he is wearing a long-sleeved/collared shirt.
In the episode Halloween it is said that Nicky Driscoll died on the Halloween before the Kennedy assassination, which would be 31 October 1963. Indeed, Angela finds a ticket stub from the dance with that year on it. However, the yearbook she checks to find Nicky Driscoll's picture is the yearbook from the year 1963, which would have been for the year before, for the class of 1963, who would have graduated in May/June of that year. Instead she finds Nicky Driscoll's picture with the phrase "In Memorium" (sic), which would normally appear in the class of 1964's yearbook, since that would come at the end of that school year. Also, the ghost dance in the gym announces that the dance is for the class of '63, another reference to the class that would have already have graduated.
In the episode Other People's Mothers during the party-planning montage, Rayanne is seen spinning around in the parking lot, and the letters on the license plates are backwards, indicating a reversal of the negative.
In the episode Life of Brian after Brian vows to never again show at Angela's house with a lame excuse, yet he does, we see Graham holding a bunch of wallpapering equipment including a blue bucket. He then drops the bucket and asks Brian to help him get it for him. A millisecond later we see Graham miraculously holding the bucket again (without Brian handing it to him), and yet another millisecond later he again doesn't hold the bucket
In the episode Self-Esteem after Jordan tells Angela to keep their meetings a secret Angela goes from wearing a sweater to another top. The door to the boiler room changes sides. When Graham comes home from the first cooking class and is talking to Patty in the kitchen the recording microphone is visible in the top of the frame. On the math quiz, Angela and Abyssinia have the answer "false" for a proof question. In a proof, one must list the steps required to prove a certain statement true. However, the teacher marked their answers as correct. The handwriting on Abyssinia's quiz is the same handwriting as that on Angela's quiz. Angela and Abyssinia both make other mistakes on their math quizzes that are not marked as incorrect, such as classifying a 140-degree angle as acute or a 79-degree angle as obtuse. Both girls label a 180-degree angle as either obtuse or acute. In truth, a 180-degree angle is neither obtuse nor acute. When Angela is handed back her geometry quiz, the grade 59 is circled, yet all the answers on her paper have checks next to them, indicating that she answered all the questions correctly. Rayanne and others dance at the Buffalo Tom show as if they are dancing to a fast song, but, "Late at Night" is what the band is playing, a slow song. When Jordan finally comes up to Angela in the last scene, Angela's hair is tucked behind her ear in one camera shot. The camera focuses briefly on Jordan, but when it switches back to Angela her hair is no longer tucked behind her ear.
In the episode Pressure a recording microphone is visible at the top of the frame when Angela speaks to Sharon after Sharon came over to return some cooking dishes.
In the episode On the Wagon Rayanne and Patty are talking in the car, Rayanne takes off her seat belt twice: once in the beginning of the conversation, and once after Rayanne says, "I guess we have something in common, huh?" When the drummer and bassist of Frozen Embryos first argue their speaking and the voice track is out of sync.
In the episode So-Called Angels after suggesting to take Angela to see Rickie in the Warehouse, Jordan and Angela are in the hallway holding hands - but they broke up in Pressure.
In the episode Resolutions when Angela sits down for a minute to talk to Jordan during the first tutoring session there is a recording microphone visible. There is also a foreign object, possibly a hair, in the shot of Angela (probably something stuck to the camera lens).
In the episode Weekend while Rayanne was pretending to be sick, you could see that her hand wasn't attached to the bed post behind her.