top of page

5 Top Mistakes to Avoid in Math Primary 2 Mass and Length Topics

primary 2 mass

As parents, understanding common mistakes in Primary 2 Math can help us support our children more effectively. When it comes to topics like length and mass, specific errors can hinder comprehension. By identifying these mistakes, we can guide our children to avoid them and better grasp these concepts. In this article, we will explore the five major mistakes children often make in length & mass questions for Primary 2 Math and strategies to prevent them.

1. Confusing Measurement Units

One of the most frequent errors is confusing measurement units. Students often mix up units of length and mass, which can lead to incorrect answers when comparing or combining measurements.

Common Misconceptions

A prevalent misconception among students is that 1m equals 1000cm, which is incorrect. This confusion often leads to significant calculation errors.

Important conversions to remember:

  • 1 metre (m) = 100 centimetres (cm)

  • 1 kilogram (kg) = 1000 grams (g)

Many students have the misconception that 1 m = 1000 cm, which is wrong.

Confusing Measurement Units

2. Misreading Scales

To accurately read scales, students must understand that they should count the gaps between the numbers, not the total number of lines. A common error is to count all the lines they see, which leads to incorrect scale readings.

Example (Mass):

Misreading Scales

Consider a scale where the mass of the milk is shown as 250g. Students should count the gaps between the numbers to determine the correct measurement.

3. Overlooking the Starting Point on Scales

Another common mistake is overlooking the starting point on scales. Students may not realise that some items do not begin measurement from zero, leading to incorrect results.

Example: How many metres is the ship?

Overlooking the Starting Point on Scales

Common mistake: Looking at the end point of the ship and thinking that the ship is 8 m long.


8 m - 1 m = 7 m

The ship is 7 m long.

Tip: When an object does not start from the 0-mark, subtract to find the length.

4. Not Writing Units in Final Answers

In story sums and other mathematical word problems, such as addition and subtraction, students are required to write the units of measurement in their final answers. Not writing the units will result in the deduction of marks, a common oversight that can be easily avoided.


Mandy used 218 m of ribbon and had 94 m of ribbon left. How much ribbon did she start with?


Mandy had 312 m of ribbon at first

Mandy had 312 m of ribbon at first.

Remember to write ‘m’ in the final answer!

5. Interpreting the Number of Items as the Number of Gaps

A frequent type of question in length problems involves calculating the distance between objects. Students often mistakenly multiply the distance between two items by the total number of items instead of the number of gaps between them.


"5 trees were planted equally apart. The distance between the first tree and the second tree was 4 m. What was the distance between the first tree and the last tree?"

Interpreting the Number of Items as the Number of Gaps

Tip: The number of gaps is always 1 less than the number of items.


Number of gaps → 4

Distance between the first tree and the last tree → 4 m + 4 m + 4 m + 4 m = 16 m 

addressing these common mistakes

By addressing these common mistakes and providing practical tips, we can help students build a strong foundation and score in the mass and length test in Primary 2. Emphasising the importance of correct unit conversions, accurate scale reading, proper use of units, understanding gaps versus items, and mastering circle-related problems will ensure students avoid these pitfalls and succeed in their mathematical endeavours.

If you're a parent of a Primary 2 student, enrolling your child in AGrader Primary Math Tuition offers numerous benefits. This comprehensive program targets students from Primary 1 to 6 and adheres to the latest syllabus set by Singapore's Ministry of Education. We ensure students have a strong grasp of essential mathematical concepts, providing a solid foundation crucial for their academic progress. 

By training students to apply these basic concepts through thinking skills and heuristics in problem-solving, AGrader helps them confidently tackle various maths problems. Thorough preparation for school examinations boosts students' confidence, ensuring they perform well and feel assured in their abilities.

training students to apply these basic concepts

Additionally, AGrader’s free after-class resources, the EverLoop Improvement System,has effectively eliminated "academic forgetfulness" in over 30,000 students. This free after-class resources is free for all AGrader students from the point of their enrolment. 

With 19 centres islandwide, AGrader is conveniently accessible for families across Singapore. Enrolling your child in AGrader Primary Math Tuition provides them with the essential tools and support needed to excel in Mathematics and build a strong academic foundation.

Join Our AGrader Community Today! (Free for all AGrader & Non-AGrader students)

Join our Telegram and WhatsApp channels to gain access to more study tips, free downloads, and much more for all subjects. 

- WhatsApp channel: 

- Telegram channel: 



bottom of page