Season 3 is the show's third and the final season of Clarence (series). The actual date as well as the actual number of episodes of the season is unknown, the season started on February 10, 2017, starting with the episode "Valentimes" and will be ending consisting of 40 episodes on June 24, 2018, with the episode ”Anywhere But Sumo”.
The 3rd season has been announced quietly without any official news about the show season rewenal, it follows after Season 2 ended with 39 episodes total, while the other episodes, such as Sumo Goes West, Clarence for President, and Clarence Loves Shoopy, were originally part of Season 2 episodes and was originally going to air between November 28th to December 2nd alongside with Merry Moochmas, but were postpone indefinitely, which apparently these episodes were seperate completely, Around between Mid to Late January, the Showrunner announced that season 3 will start on February 10th, with two new episodes (Sumo Goes West and Valentimes), following a week after Pizza Hero (a season 2 finale episode)
On March 30, the show was not mentioned nor listed at the Cartoon Network Upfront 2017-18, an indication that is official that Season 3, is the last season of Clarence (series)
Also the voice recording of the season is completed  as of March 31, 2017,  as Spencer Rothbell stated that the remaining sets of episodes will air through until 2018. 
As said for Season 3 had a small significant changes, between Sumo and the other two kids, who had changed schools, and also will feature a few guest stars cameo, introducing some new or returning characters and will also episodes that focuses on some characters and more holiday specials such as more with Halloween and Thanksgiving
On October 19, the series production had been finalized its completion, the series will end with over 133 episodes.
In 2018, the last 15 episodes had aired in Asia and Australia in January, February in Latin America, and April in Europe, The series had ended with the episode, Anywhere But Sumo.
It’s school election time at Aberdale Elementary, and Jeff is once again determined to become Class President. However, like previous years, he’s unsuccessful in connecting with other kids, that is until he sees a shoe-in puppet President, the lovable Clarence!
Clarence plans to throw the sleepover to end all sleepovers with decorations, pillow fights, and games, but there's one thing missing - guests; Clarence wants invite all his friends, but finds that they might need some convincing.
During the storm, Clarence goes out to get Jeff a raisin drink. While gone, Jeff has to stay in the house with Chad and Mary, and eventually goes crazy about having the house cleaned. They later set out to find Clarence.
While trying to get to California for vacation without telling Clarence, Miss Baker gets trapped in the store with Clarence, the Mayor, Meg (the substitute teacher) and one of Jeff's moms. The four get suspicious of Meg and try to leave the store.
As the storm gets worse, everyone gets stuck in the school's gym and eventually fight. After Clarence gets them to get along, the big flood occurs and everyone works together to block the flood from entering the school.
The boys go the Aberdale Community Pool for a day of wet fun; Jeff wades in the shallow end; Sumo tries to conquer the diving board, redeeming himself from last summer's bellyflop; Clarence sneaks past the lifeguards into the hot tub.
After surprising Clarence with Martial Arts classes at the Aberdojo, Mary gets talked into joining the class herself. She loves the slow-paced lessons in discipline and control, but Clarence just wants to have fun and kick butt.
Clarence finds a fast friend in JT, who shows him some cool new music, a new outlook on life, and a sweet rat-tail; Clarence leans into the rat rail lifestyle, discovering a whole new side of Aberdale he never knew existed.
Clarence feels the call of the wild – and decides to live a life free of the hustle and bustle of the modern world. He sets out to find a place to live his feral life, but soon realizes he lacks some basic survival skills.
After Clarence accidentally knocks Belson’s new video game down a storm drain, Belson enters the large underground sewer tunnel to retrieve it. When Belson doesn’t return, Clarence must decide whether or not to go in after him.
Clarence throws a big talent show in his yard to showcase all the fun hidden talents of his friends. But when Brady claims he’s talentless, Clarence sets out to prove that everyone has something special to share!
Mary buys a new trampoline for the family, but an accident lands her on the couch for a while. Determined to fight the boredom of being stuck indoors, she discovers her neighbor may be hiding something exciting.
When Clarence starts to play around with his home video camera, he becomes drawn into the world of filmmaking. From talking toys, to real actors, to documentary subjects, Clarence is determined to find the right style to tell his story!
Clarence is in disbelief when he learns his best friend Belson has a new girlfriend named Pipi. But when he observes their less than romantic behavior, he decides that he needs to teach them the ways of love to help keep their fling afloat!
After a marathon of classic sitcom episodes, Clarence becomes stuck as alter-ego “Clarry,” an obnoxiously overacting sitcom version of himself. It’s up to his friends and family to help him snap out of it, or face life with a new Clarence.
Clarence submits a short story into a writing contest. He’s overjoyed when he learns he’s accepted as a finalist! When Jeff finds out Clarence has to attend a formal dinner, he fixates on transforming the messy Clarence into a gentleman.
Clarence, Jeff, and Sumo visit their local video store to rent a movie, but discover it’s all rented out! Each of them have a different idea of what tape to bring home, and must enlist the help of a tie breaker to figure it out.