We find Mildred walking through the forest on the first day of school, trying to find her way so she can make it on time. Ethel (who can already fly a broomstick) flies up behind her, and taunts her, reminding her that she wouldn't want to be late on the first day. Mildred accidentally hits Ethel in the face with a tree branch, though Ethel thought she did it on purpose. When Mildred arrives at the school (late), the gate is locked and so she has to try and fly over it on her broom, crashes horribly, breaking her broomstick and making a rather poor introduction for herself. Maud takes a liking to Mildred and decides to help her pass the upcoming broomstick-flying test, and she needs the help considering she's scared of heights (and the dark!). A virtual reality broomstick flying training machine arrives at school, and so Mildred, Maud, Jadu and Ruby sneak down in the middle of the night to practice.

Mildred and her friends can hardly stand the food they're given to eat at lunch, and she gets caught trying to dump it in the garbage bin by Miss Hardbroom (by spilling it all over her!) Miss Hardbroom of course takes the issue to Miss Cackle, who decides that she should eat whatever the girls are given to eat. Mildred finds herself in the kitchen, and finds out that the cook is able to make incredibly good food (including pizza!) but isn't allowed to because of school policy. Miss Cackle decides that the food the girls are getting is barely edible, and so sneaks down to the kitchen at night to have some pizza herself. In the end, Miss Cackle declares Saturday to be 'pizza day' and Mildred is applauded as a hero by the other girls.

The witches' cats arrive, but they're one short.... The caretaker's nephew, Charlie, visits the academy, but he doesn't believe that the witches are real.... Mildred ends up turning Ethel into a pig, which was bad enough, but it was suppose to have been a frog! Ethel then gets mistaken for an escaped pig from the local farm so she is taken there. The only person who knows the reversal spell is Charlie so he and Mildred rush to the farm to save Ethel. When they find her, Charlie casts the spell, but it ends up making Ethel go a little quackers....

This is the first of a two-parter. Mildred fails a potion test, she was supposed to have made a laughing potion but instead, because she believed the potion should have been green, she ends up making an invisibility potion. She is sent to Miss Cackle to explain. Mildred then decides that it's time to buck her ideas up and to make an effort to improve, which she does by passing the following potion test successfully. For the upcoming Hallowe'en celebrations, Mildred's class has been asked to put on a broomstick display. However, only one of them actually has to fly in it, and Mildred is the one who is chosen. Her broom, which was damaged during her crash landing on her first day, isn't up to the job, so Ethel lends Mildred hers, but she has evil intentions. At the display itself, Mildred crashes into the Grand Wizard, but it wasn't her fault! Ethel had instructed her broom to make Mildred look stupid deliberately...

Mildred finds that not all of the witches in town are from the academy, some evil ones have shown up and are planning to take over the academy by turning everyone into frogs whilst they're asleep. They discover her and they cast a spell on her making her unable to move. When they're gone, Miss Drill comes to help her.

It's the start of the summer term, and it begins with Mildred having a dream that she is being put on trial for being the worst witch. A new girl, Enid Nightshade, joins the academy, and Mildred is asked to show her around. However, this leaves little time for Mildred to spend with Maud. Enid ends up getting Mildred into all sorts of trouble. Then Mildred discovers a monkey coming from Enid's room. It turns out that the monkey is really a bit of a pussycat....

Mildred is warned that if she doesn't behave, she may not be allowed to go on the half term trip. Mildred does her very best to behave. No one believes she can manage it. On the last day before the trip, Mildred feels that she can do it. It's also Miss Cackle's birthday. Just before they enter the hall for the celebrations, Enid drags Mildred into a cupboard and Ethel locks the door. Mildred is upset, as she now believes that she won't be going on the trip after all. They see a window from which they might be able to escape, but it's too high. They find an old broomstick and decide to fly out. The window ends up leading straight to the hall where the birthday celebrations are taking place!

Mildred and the girls are forced into the woods by Miss Drill and Miss Hardbroom for their half term trip. Arriving at their campsite, they find it occupied by Rocky Mountain Rangers, with whom they share it. The two groups also share in each other's activities. Although the trip is intended to be magic free, Ethel's evil heart once again forces Mildred's friends to fight back, and chaos ensues....

Miss Hardbroom and Miss Bat have a falling out. Miss Cackle magics up a drink for the witches, and then sets them the task of recreating the drink, but they aren't allowed to use magic. The witches try everything of which they can think, even cheese! Eventually, Ethel and Drusilla decide not to work with the others and try to do it by themselves, but using magic. The others wonder whether or not flowers could be used to make the drink. With the help of Miss. Bat they find that they can and proceed to make the delicious drink! But, the night before the tasting, Ethel and Drusilla put something hot into the others drink.... On the day of the testing, the drink made by Mildred and her friends doesn't go down to well. However, Ethel's and Drusilla's does go up quite well, with a little help of the Dr. Foster effect.

Mildred is looking after 'Bonzo', who is Ruby's cyberpet (well, at least it isn't one of those ruddy Tamagotchis!). After the potion lab is destroyed, Bonzo goes missing.... Ethel's dad, who's on the board of directors, visits the academy, and convinces the teachers to set up a computer system. Bonzo makes his return, but he has been affected by magic as a result of the potion lab's destruction.... Bonzo connects up to the computer system and uses it to hypnotize everyone to try and help him take over the world when the system is connected to the net.... Mildred, with some help from a third year, are able to break Miss Hardbroom from the spell who then proceeds to defeat Bonzo just in time!

After being foiled in a plot to steal sweets from Mildred and her friends, Ethel decides to lure them to an out-of-bounds tea room in the woods to get even. The girls meet a nature-loving businessman named Sam, who has trouble standing up to his overbearing boss. Meanwhile, Miss Cackle is already at the tearoom, but she can't let Miss Hardbroom find her.... When they find out about Sam's role in a web of deceit to swindle the tearoom's owner out of her land, they also find out that his boss is planning to build a polluting factory on the land! They then help Sam stand up to his boss by driving Sam barking mad. And after avoiding the wrath of Miss Hardbroom they gorge themselves on sweets!

The Grand Wizard visits the academy to give a lecture, and he's accompanied by three trainee wizards, one of whom, ""Loppy Luggs"", could be described as the Worst Wizard.... The trainee wizards decide to make their visit into a boys vs girls affair.... During the lecture they cast a spell which makes some of the girls raise their hands but then become unable to speak. Mildred ends up firing a rubber from a ruler, which hits the Grand Wizard's head! She is then sent to her room.... The teachers organize a debate between the wizards and witches to find out who is better. The wizards get Loppy to make a potion which will give them an unfair advantage.... Mildred finds that she's left her potion book in the potion lab and so goes there to get it. There she finds Loppy, who is really called Merlin.... She finds out from him what the wizards are up to. The potion they made helps them to speak more confidently! She takes some of the potion and enters the hall where the debate is t

It's the end of the year for the student witches, and Mildred's incantations still don't seem to work as well as intended. To cure a case of hay fever brought on by one of Mildred's errors (""Exfoliatus!"" ""A CHOO!"") the other teachers give Miss Cackle what they assume to be a remedy potion, but which is in fact a mislabeled experiment of Miss Hardbroom's. The other teachers make no mention of the mishap, even when Miss Cackle's behaviour takes a turn for the malicious. It is Mildred and company, however, who realize that it is not Miss Cackle, but her evil twin back to cause more trouble. Mildred saves the day, for which she earns a raise in her final grade from C-- to A+.