The Best Teacher is the seventh episode of The Worst Witch (2017 TV Series). It was first broadcast on CBBC and CBBC HD on 15 February 2017. It is preceded by The Great Wizard's Visit, and Followed by Maud's Big Mistake.
Mildred and Maud want to use the Magic Mirror to speak to their parents, but there's a queue. Esmerelda Hallow comes out, having spent ages talking to her mother, and Ethel goes in, only to find that their mother doesn't have time to talk to her.
Mildred worries about failing the witching history test the next day, so Enid suggests a wisdom spell, despite Maud's protests about it being against the code. They need a hundred year old sock for the spell, which they sneak from Miss Bat's feet while she's sleeping. Miss Bat wakes up claiming something has taken her sock, and Miss Cackle and Miss Hardbroom decide that she has 'lost her marbles' and that she needs some time off teaching.
The next morning, Mildred wakes up to find that instead of making her wise as in smart, It's made her wise as in old. Maud goes to the library to find a way to turn Mildred back, but Esmerelda tells her that a wisdom spell can't be undone, you have to wait for it to wear off.
On the way back from the library, Maud meets Miss Darkside, the replacement teacher for Miss Bat. Miss Darkside asks to meet Miss Cackle, so Maud tells her that Mildred is Miss Cackle, and Mildred tells Miss Darkside that she is not needed anymore, causing her to leave, and they then introduce Mildred to Miss Cackle as Miss Darkside. They explain Mildred's absence by saying that Mildred's mother is ill (with a problem toenail) and Mildred had to go home to look after her.
Mildred then goes to teach Miss Bat's history class, where she sits in her own desk before realising she's supposed to be the teacher. She asks the class what Miss Bat usually does, and Felicity Foxglove says 'fall asleep'. Maud suggests that they prepare for the test. Miss Hardbroom then comes in and introduces herself to 'Miss Darkside' and comments on Miss Darkside's reputation. Mildred asks Miss Hardbroom what she's heard about 'her' reputation. Miss Hardbroom says that Miss Darkside is 'One of the greatest disciplinarians of the witch academy network, famed for upholding tradition, demanding order and instilling fear'. It's clear that Miss Hardbroom admires Miss Darkside.
Drusilla makes fun of 'Miss Darkside's' earlier stuttering, and Mildred sends Ethel and Drusilla out of class, pleasing Miss Hardbroom. Miss Hardbroom leaves, and Mildred, assisted by Maud and Enid, does an interactive telling of stories from the history book. In the staffroom, 'Millicent Darkside' is introduced to the other teachers. Algernon Rowan-Webb and Miss Cackle discuss whether Miss Bat may need to leave permanently, as she's still talking almost entirely about socks.
Ethel, thinking that Mildred is faking her mother's 'illness' to skip the test, drags Drusilla to Miss Cackle's office, where they ring Mildred's mother, and Drusilla pretends to be Miss Cackle, to find out that Mildred is not at home. Meanwhile Mildred and Maud distract the real Miss Cackle to keep her from calling either Mildred or her mother. Miss Hardbroom then turns up with a pile of marking and the test papers and answers for 'Miss Darkside'.
Ethel goes to 'Miss Darkside' to tell her that Mildred is skipping the test, but 'Miss Darkside' says she has been told about Ethel's 'tall tales'. Ethel says that she's not a bad girl, and that she works really hard, and that wishes it came naturally to her, as maybe then her mother would half as interested in her as her sister, Esmerelda. Miss Cackle then appears, and decides to call Mildred's mother and find out what is going on.
Mildred decides to own up and tell the truth, but as she is about to enter Miss Cackle's office, she turns back into herself. She tells Miss Cackle that she is Mildred Hubble, to which Miss Cackle says, "yes, we can see that, dear," and Mildred realises that she's changed back. Miss Cackle and Miss Hardbroom question Mildred as to where she has been, while Maud hurries to cast a spell, which requires toenails that she takes from a sleeping Miss Bat.
Miss Cackle summons Mildred's mother, who comments that Miss Cackle only called an hour ago. Maud casts her spell, which gives Mildred's mother ingrown toenails. Miss Cackle sends her back, and Miss Bat comes running in, claiming that something is 'tinkering with her toenails', and that she'd like to return to teaching because it's safer. Miss Hardbroom says that won't be possible because they have a capable replacement, but Mildred says that she just saw the replacement witch leaving and was coming to tell Miss Cackle.
In History class, Maud comes top of the class in the test, while Ethel comes fourth-top, Drusilla comes bottom and Mildred is second-bottom, which she says is the greatest moment in her life, because she's only the second worst witch for a change. Miss Hardbroom and Miss Cackle then come in and say that someone has been impersonating a teacher- but it's Drusilla who gets in trouble, for ringing Mildred's mother and pretending to be Miss Cackle.
Later, Ethel hears Maud talking about wisdom spells, and realises that Mildred was Miss Darkside, but Mildred points out that Ethel and Drusilla impersonated a teacher too. Maud says that her spell was only supposed to work on witches, yet it worked on Mildred's mother, leaving them to wonder if she could actually be a witch.