Year 1 Mathematics · AC9M1M02
Length can be measured with informal units, but the units must be the same size and placed end-to-end without gaps or overlaps
Ready to project and teach
Length can be measured with informal units, but the units must be the same size and placed end-to-end without gaps or overlaps.
Learning routine: Choose unit → Start at end → No gaps → No overlaps → Count units
Mixed-size units cannot give a reliable measure.
The final count tells how many informal units long the object is.
Explain your thinking: Say what each part of the model represents, then explain why the answer or conclusion follows.
▭▭▭▭▭ 5 same units no gaps
start at edge touching units count all units
Paperclip measure Measure a pencil with equal paperclips placed end-to-end. Model: clip clip clip
Find the mistake Look for gaps, overlaps or different-sized units. Model: gap = not fair
These curriculum examples extend the central model into varied contexts. They are learning contexts, not extra definitions to memorise.
using 2 different units; for example, pop sticks and pencils, to measure the length of an object such as a desk, and explaining why the number of units used may be different
Try and explain: The same strip measures six long blocks or twelve short blocks, with no gaps. Did the strip change length?
No. Smaller units require more copies. The count depends on the unit as well as the object's length.
comparing the length of 2 objects such as a desk and a bookshelf by laying multiple copies of a unit and counting to say which is longer and how much longer; explaining why they shouldn’t have gaps or overlaps between the units as this will change the length of the unit
Try and explain: A mat measures eight identical blocks and a tray measures five. How much longer is the mat?
Three blocks longer: 8 − 5 = 3. Both measurements must use the same-sized blocks placed end-to-end.
measuring the distance between 2 locations using footsteps, comparing the results and explaining why there may be different results; for example, referring to the different length of footsteps as using different units
Try and explain: Two children count different numbers of footsteps over the same path. Give a possible reason and a better comparison method.
Their steps may differ in length. Use copies of one fixed unit, such as the same measuring strip, for a more consistent comparison.
measuring and comparing the length of objects using blocks; for example, comparing the height of 2 toys by stacking blocks one on top of the other and counting how many it takes to reach the height of each object to decide which is taller
Try and explain: One toy reaches six stacked blocks and another reaches four. Which is taller, and by how much?
The first is two blocks taller, provided the blocks are identical and both stacks start at the same level.
Measure length with equal informal units placed end-to-end.
A strip is covered exactly by 6 equal cubes in a straight row. How long is it?
Watch for this mistake: Six large units and six small units do not show the same length. Counts can be compared directly only when the units match.
A child leaves spaces between five cubes while measuring a pencil. What must be fixed?
Check the joins between the units.
Move equal cubes end-to-end without gaps, align the start, and measure again.
The same ribbon measures 8 small blocks or 4 longer blocks. Must one measurement be wrong?
Consider the size of the units.
No. Longer units need fewer repetitions to cover the same length.
Key idea: Length can be measured with informal units, but the units must be the same size and placed end-to-end without gaps or overlaps.
Return to the concept model if an answer is uncertain. Use the model to explain, not just to guess.
Use the Practice Sheet for written or hands-on work, Practice for supported feedback, and Test when the student is ready to demonstrate independent mastery.
Length can be measured with informal units, but the units must be the same size and placed end-to-end without gaps or overlaps.
Learning routine: Choose unit → Start at end → No gaps → No overlaps → Count units
AC9M1M02: measure the length of shapes and objects using informal units, recognising that units need to be uniform and used end-to-end
Explore optional teaching slide packs for classroom lessons and explanations at home.
Browse Teach & Explain · Browse Print & Go
Teachers: follow SkillrHub on TPT, then email us to request a free sample before buying. Include the year, subject and topic or curriculum code.
After trying the sample, honest feedback is welcome. A TPT review is optional, where available, and does not need to be positive.