Common Errors Made Past Times Maths Teachers

I've of late started working with a couplet of trainee maths teachers. It's already proving to endure a useful sense for me - I'm certain it volition conduct maintain a positive acquit upon on my teaching. It's fascinating to sit down at the dorsum of the classroom with my students. 

There's been a couplet of moments lately where I've seen a trainee instructor tell a course of pedagogy something that's non quite right, or that I've felt has needed farther clarification. It's interesting to run across how a teacher's plain of written report noesis - peculiarly their noesis of mutual misconceptions - develops rapidly over the commencement few years of their career.

I've started to line together a listing of some of the mistakes or oversights that I've seen both inexperienced as well as experienced maths teachers make. I'd endure interested to withdraw heed what you've seen every bit good - delight permit me know thus I tin hand notice create a comprehensive listing that volition endure of role to trainees as well as NQTs. 

Square root
The foursquare rootage symbol denotes exclusively the positive root. So if yous write √9 = ±3 on the board, you've made a mistake.
Source: Wikipedia
If you're solving the equation x2 = nine as well as thus of course of pedagogy at that topographic point are 2 solutions - both positive as well as negative 3 locomote here. You're non wrong nearly that. But brand certain yous role the radical sign correctly.
   
Angles
What angle fact is depicted below? Some of my students conduct maintain been incorrectly taught to say 'angles inwards a circle amount to 360o'.  It should endure 'angles roughly a dot amount to 360o' (as per GCSE grade schemes) or 'angles inwards a total turn/revolution amount to 360o'.

Whilst we're on the plain of written report of angles, I've exclusively of late constitute out that proverb 'angles inwards a triangle are supplementary' is wrong. Supplementary agency that 2 (and exclusively two) angles amount to 180o.

Prisms
I don't recommend scream for maths teachers on Twitter whether a cylinder is a prism! I did that in 1 lawsuit - the declaration went on for days as well as I was none the wiser every bit a result.
Since this Twitter conversation, I avoid defining a cylinder every bit a prism inwards illustration I'm wrong, exactly I exercise tell my students that nosotros bring out the book of a cylinder inwards the same way nosotros bring out the book of a prism.

Interestingly, the GCSE formula canvass uses a controversial film of a prism.
Frustum
It's a frustum, non a frustrum. This give-and-take is oftentimes misspelt.
The gild of operations
Try this question: 3 - 3 x 6 + 2.

If yous don't acquire an response of -13 as well as thus yous demand to await in 1 lawsuit to a greater extent than at the gild of operations. The unhelpful acronym BIDMAS (which incorrectly implies that yous should add together earlier yous subtract) confuses some teachers every bit much every bit it confuses students.

Vocabulary
I of late observed a lesson on angles inwards polygons with a Year 8 class. The educatee instructor asked the lift of a vii sided shape as well as a man child pose upwardly his manus as well as said it was a heptagon. The instructor said he was correct, as well as thus moved on. She didn't notice that some other man child was rattling bothered yesteryear this. He angrily protested to the students roughly him. I watched from the back. This man child had been taught that a vii sided shape is called a septagon - which is also right - as well as he idea that the instructor had made a mistake. At commencement he was angry, exactly as well as thus he doubted himself. His confidence took a knock. Later inwards the lesson, when the chance arose, I reassured him that both damage are acceptable. He was relieved. He felt vindicated. It was a pocket-sized fry oversight yesteryear the instructor exactly it had quite an acquit upon on this student.

I in all probability exercise things similar this every bit good sometimes. We say things that, rightly or wrongly, differ from what students conduct maintain been taught previously. This causes confusion as well as mistrust.

I'd endure interested to know what mistakes as well as oversights you've seen teachers make, thus delight comment below or tweet me thus I tin hand notice line together a comprehensive list. We're ever talking nearly the importance of students learning from each other's mistakes, thus let's exercise the same.