A turn just flips the signs. So (3,5) turned becomes (-3,5).
For a 90° turn about the origin, the child only changes the signs but leaves x and y in their old spots. They rotate (3,5) and get (-3,5) instead of swapping to (-5,3). They forget that a quarter turn moves the x value into the y spot and the y value into the x spot.
The child learned that turns flip signs, like a reflection or a 180° turn. So they reach for the same sign trick here. They never learned that a 90° turn also swaps the two numbers. Swapping feels like a separate, harder rule, so it gets dropped.
This one responds to correction in the moment — the idea is there, the rule being applied is not.
Rotates 180° by negating only one coordinate
What you might hear
Half a turn flips it across. So (4,7) becomes (-4,7).
For a 180° turn about the origin, the child flips just one number's sign. They rotate (4,7) and get (-4,7) instead of (-4,-7). They treat a half turn like a reflection over one axis, changing only the x or only the y.
A 180° turn looks like flipping the point across an axis to the child. Reflections change only one coordinate, so they copy that habit. They do not picture the point swinging all the way to the opposite side, where both signs must change.
This one responds to correction in the moment — the idea is there, the rule being applied is not.
Dilates by adding the scale factor
What you might hear
Scale factor 3 means add 3. So (2,5) becomes (5,8).
For a dilation centered at the origin, the child adds the scale factor to each coordinate instead of multiplying. With scale factor 3 they take (2,5) and get (5,8) instead of (6,15). They turn the stretch into a slide.
The child knows a dilation makes the figure bigger. Adding a number makes coordinates bigger too, so it seems to fit. They confuse multiplying by a factor with adding it. The word scale does not yet mean times for them.
This one responds to correction in the moment — the idea is there, the rule being applied is not.
What to say when you see it
For each mistake above, Algo School gives you the words to say next — the specific response that corrects the thinking instead of just marking the answer wrong, plus practice aimed at that exact error.
The point (2, 3) is translated by adding 1 to the x-coordinate and adding 6 to the y-coordinate. Find the image, for Olga.
A(1, -3)
B(8, 4)
C(3, 9)
D(2, 18)
AnswerC — (3, 9)
Generated by coordinate-plane-8, a deterministic question engine — not written by an AI, and verified before any child sees it.
FAQ
Questions parents ask about this
How do I know which of these mistakes my child is making?
Look at what they SAY, not just what they wrote. Each mistake above includes the phrasing a parent typically hears — that sentence is usually the giveaway. In Algo School, the tutor recognises these patterns while your child is working and adapts the session around the one it sees.
Is "Describe transformation effects on coordinates" something children normally struggle with?
Yes. We track 3 distinct approved mistake patterns for this concept, each one written up because it recurs — not because it is unusual. A child making one of them is doing something systematic, which is far easier to fix than random errors.
What should I do once I know which mistake it is?
Respond to the thinking, not the answer. Algo School gives parents the specific wording for each mistake, then generates practice targeted at that error and shows you whether it actually cleared.
Where do these mistakes come from?
They are part of the same content library that drives practice: each one is reviewed and approved before it is used, and the Geometry questions on this site are checked by an automated verification pass before a child is ever served them.
Related
Other places children go wrong
Where this sits
The year this concept belongs to
See the full curriculum map — every Common Core concept we cover, the
verified question count, and what a child at this level should know.
Find out which one it actually is
Free for 15 days — a card is kept on file, but $0 is charged until
the trial ends. Cancel in one click before then and pay nothing.