Watch your speed
0
Overview
Using this Resource
Connecting to the Curriculum
Marking Student Responses
Working with Students
Further Resources
This task is about reading a speedometer.
The speedometers show how fast a car is going at a race track.
Look at the speedometers.
Write what speed they are showing.
Task administration:
This task can be completed with pencil and paper or online (with auto marking displayed to students).
Level:
3
Curriculum info:
Keywords:
Description of task:
Students read scales from a car speedometer.
Curriculum Links:
This resource can help to identify students' understanding of reading linear scales.
Learning Progression Frameworks
This resource can provide evidence of learning associated with within the Mathematics Learning Progressions Frameworks.
Read more about the Learning Progressions Frameworks.Answers/responses:
Y6 (03/2016)  
a)  30  very easy  
b)  0  very easy  
c)  230  easy  
d)  135  easy  
e)  95  very easy  
a)e) 
All 5 correct  moderate (52%) 4 +  easy (70%) 
NOTE: Accept within +/ 2 km/h. Students who identify more detail than the increments or half increments are indicating the importance of more precision, and may be "more correct": For example the needle may well be pointing more toward 96km/h than 95km/h for queston e).
Teaching and learning:
This task is about reading a scale (or gauge) where each mark represents 10 km/h and written labels are 40 km/h apart. A key understanding is about identifying the size of the increments, and then using this to derive answers that are between the marks (either half or close to half way).
Diagnostic and formative information:
Common error  Likely reason  
a)
c) d)
e)

35
215
125128
88

Deriving incorrect units from the scale
Students interpret the size of the spaces on the scale as 5 km/h rather than 10 km/h. With this assumption question a) is one space less than 40 km/h (35 km/h), question c) is three spaces more than 200 km/h (215 km/h), and question d) is one space more than 120 km/h (125 km/h). Some students also made an adjustment to this misconception to get 126 km/h 128 km/h for d) and 88 km/h for question e).

a)
d)

39
121

Students interpret the size of the spaces on the scale as 1 km/h rather than 10 km/h: one space less than 40 km/h is 39 km/h, and one space more than 120 km/h is 121 km/h.

d)
e)

125
90 or 100

Accuracy
Students may think that reading a scale is sufficient if it is read to the nearest mark. This means that any measrure between marks is not estimated and incorporated into the answer. This could also be called being "too general" with reading the scale.

Next steps:
Deriving incorrect units from the scale
Students who derive incorrect units (either 1 km/h or 5 km/h spaces) from the scale (speedometer) may need to recheck their assumptions by counting the marks up and down using the labelled marks, and then unlabelled marks on the speedometer. This may help reinforce that the marks represent the size of the space, enabling them to interpret the scale. Students could also work on a printed copy of the resource and label all the marks.
Ideally, students will have already explored creating their own scales, and measuring real objects using a variety of scales. This can build a foundation of understanding about how scales and measurement units are constructed, and develop the idea that the spaces (units) are nonoverlapping, and the scale is built up with the iteration of the units.
Note: vocabulary is important here and words like spaces and marks help students to express that this is about nonoverlapping measurement units, not just about counting numbers, and can help students understand what they are counting (marks or spaces).
Students could also be asked about zero (the first mark). The idea of starting from zero rather than 1 is somewhat different to counting, as is the idea that they are increasing the measure with a nonoverlapping measurement unit. If they count the marks back from 40: 302010 they may recognise this as zero. They can then then work back up the marks to reinforce the size of the space as 10km/h. Students could also be asked how what each space represents, i.e., how many km/h more each mark represents.
Accuracy
Once students have an idea about the size of the spaces, they can then explore the space in between the marks, starting with estimating what number is half way (5 km/h) and then what is a quarter of the way (2 km/h or 3 km/h, or 2.5 km/h). They could then confirm that their guess for the value doesn't exceed the value of the next mark.
Some students might need to be asked to continue checking where the needle is pointing, and make sure they realise the importance of accuracy (e.g., the difference between 100 km/h and 105 km/h could be significant).