Originally, Zack and AC were written to be bitter rivals for Kelly's romantic affections. Off screen, however, Mario Lopez and Mark-Paul Gosselaar were (and continue to be) very close friends. The writers, sensing the obvious chemistry between the two actors, had the characters re-written as best friends, and they remained that way for the rest of the show.
Series creator and executive producer Peter Engel did not know that Dustin Diamond was only 12 when he cast Screech and later angered Diamond by repeatedly noting his immaturity relative to the other and older regular cast members. Engel also said that he would not have cast Diamond if he'd known his age at time.
The set of the school was never struck down completely after the show stopped production. It has been used and redressed on many shows that air on the Disney Channel and Nickelodeon since then, such as That's So Raven (2003) and iCarly (2007).
Elizabeth Berkley originally auditioned for the role of Kelly Kapowski and was turned down in favor of Tiffani Thiessen, but the producers liked Elizabeth so much that they created the Jessie Spano character especially for her to play.
The working relationship between Dustin Diamond (Screech) and the rest of the young cast was reportedly so bad, that not only was Diamond not invited to the photo shoot and cover story that PEOPLE magazine did for the show's 20-year anniversary in 2009, but Diamond's picture was cropped out of an 1989 group photo of the cast; ironically, Dennis Haskins (Mr. Belding), the only cast member with whom Diamond is still on good terms, was not invited to join the 2009 group either, but he did participate in a reunion sketch on The Tonight Show Starring Jimmy Fallon (2014).
The final graduation episode had already been shot when the network ordered additional episodes. Tiffani Thiessen and Elizabeth Berkley were attached to other projects by that time, necessitating the creation of a replacement character Tori, who was played by Leanna Creel. The Tori episodes aired in the middle of the other final season episodes to sidestep continuity problems; the Tori paradox was based on the idea that Tori, Kelly, and Jessie were all at Bayside at the same time and simply had different classes and different social interactions with Zach, Slater, Screech, and Lisa that never overlapped.
The series is notorious for frequently introducing new characters who subsequently disappear in later episodes. Some of the more glaring examples of characters who fall victim to this trend are Jessie's new stepbrother, Eric Tramer (Joshua Hoffman), who, after making peace with the gang and agreeing to live with Jessie permanently, is never seen or spoken of again; Violet Bickerstaff (Tori Spelling), Screech's girlfriend, who disappears mid-way through season 3; and Laura (Jennifer McComb), a homeless girl and Zack's love interest from the two-part Christmas episode, who is to live with the Morris family until her father finds a job, but who is never seen or referred to after these episodes. However, the most obvious example is Tori Scott (Leanna Creel), who transfers to Bayside at the beginning of season four and appears sporadically throughout the season, but she disappears before the graduation episode. Her fate was never revealed.
When "Saved by the Bell" was run in syndication, several episodes used re-edited footage from Disney Channel's Good Morning, Miss Bliss (1987) episodes as flashbacks. The segments in which Zach remembered his junior high school years were added to the beginning of these episodes.
Although the five friends were supposed to be the same age, Dustin Diamond was actually 12 years old when the series started. Elizabeth Berkley was 17 and the rest were all 15. Only Diamond was still at high school age at the end of the series.
According to producer Peter Engel, at a meeting before the show had been created, NBC President Brandon Tartikoff suggested the show be given a name that used the word bell (such as "When the Bell Rings"). One of Engel's colleagues then suggested the name "Saved by the Bell," which Tartikoff liked. Engel disliked the name but, believing that someone else probably owned the rights to the phrase, went along with it. As luck would have it, NBC's legal department discovered that nobody owned the rights to the phrase, and, by the next day, Engel's office was covered in large banners that said Saved by the Bell.
On February 4, 2015, original cast members Elizabeth Berkley, Mark-Paul Gosselaar, Dennis Haskins, Mario Lopez and Tiffani Thiessen appeared in a reunion sketch on The Tonight Show Starring Jimmy Fallon (2014). The sketch featured Fallon as a student at Bayside High, with the show's original sets reused and many of its most famous moments spoofed, including Berkley's infamous "I'm so excited!" line from the episode Jessie's Song. However, Dustin Diamond and Lark Voorhies' did not appear. Diamond's absence was alternately explained by a previous work engagement (he was doing a comedy show on that day), his recent arrest in Wisconsin after a bar fight where he was accused of non-fatally stabbing a man, and his poor relationship with the rest of the cast. Voorhies' representative said she was hugely busy with work and did not participate because she had no time.
This show follows Good Morning, Miss Bliss (1987), which took place at John F. Kennedy Junior High School in Indianapolis, Indiana, but was canceled after 14 episodes. NBC retooled the show, gave it its new title, moved it to Bayside High School in Pacific Palisades, California, and removed many of the characters. Dennis Haskins (Mr. Belding), Mark-Paul Gosselaar (Zack Morris), Dustin Diamond (Screech Powers) and Lark Voorhies (Lisa Turtle) were the only actors/characters to make the transition from GMMB to "Saved by the Bell". No explanation was ever given as to why only these four characters moved to California. This has led to a fan theory that SbtB is actually an elaborate daydream by Zack Morris during his GMMB years, where he is a slacker but fantasizes about himself being the cool kid in SbtB who always succeeds and gets away with everything. Supporters of this theory point at the lyrics of SbtB's theme song (which supposedly describe 'slacker' Zack's thoughts), and to Zack's ability to do a "Time-out" (where he temporarily stops time and breaks the fourth wall).
Mark-Paul Gosselaar originally considered "Running Zack" to be his personal favorite episode of the series. However, in November of 2016, he changed his opinion of it. Calling it insensitive to Native Americans and also apologizing for it.
In the early 1990s, reruns of the show were being watched by an average of over 4 million viewers on the TBS cable station; this was equivalent to around 40 million viewers for programs airing in prime time on major networks.
According to executive producer Peter Engel, A.C. Slater was originally intended to be a John Travolta-type character. When finding a satisfactory white actor proved difficult, Engel asked casting directors to look for Latino, Asian, and Black actors as well. Mario Lopez subsequently won the role.
Casper Van Dien made several uncredited appearances throughout the show's final year. He has one line in one episode and is often seen just as a simple background extra, mostly in hallway scenes by the lockers.
In the season 3 and 4 DVD boxed set released by Lion's Gate in 2005, there is a still photograph taken from the episode "No Hope with Dope," with the gang alongside NBC chief Brandon Tartikoff. However, the photograph was badly edited, with Mr. Belding's (Dennis Haskins) head superimposed over Tartikoff's.