Different sized capacities
When ordering these capacities it is important to look at two things:
 the ordering of all the measures in relationship to the other measures; and
 the method or strategy that students used to order the measures.
Bearing this in mind supports students with their next steps. Giving a cumulative score for the number of parts of the question the student gets correct does not appear to give as useful an indication of a student's specific knowledge of capacity as looking at responses to the different containers.
Y8 (10/2010) 

a) 
5ml

very easy

b) i) ii) 
0.5L is larger than 50ml Accept explanations that correctly describe or infer the relationship between litres and millilitres such as:

difficult very difficult 
Based on a representative sample of 191 Y8 students.
This assessment resource is about being able to order a range of capacities in millilitres and litres. It involves understanding the relationship between litres (the units) and millilitres (the subunits) and working (or converting) between them. It also involves understanding or knowing the size (capacity) of the given measures.
For part a) students may order the millilitre capacities from smallest to largest and then the litre capacities, but not know how to work between millilitres and litres (some way off understanding the relationship between millilitres and litres). This is not comparable to a simple substitution or transposition error, but shows they understand the relationship between litres and millilitres.
For part b) a significant number of students thought that 50ml and 0.5 L were equal, which, amongst other misconceptions, suggests they thought that 1L = 100ml. Other students indicated that 0.5 L was [always] bigger because litres are bigger than ml (insufficient argument).
See Student work samples [pdf] for examples of the different student strategies.
Common response  Likely misconception  
a) b) i) ii) 
5ml  250ml  1250ml  0.75L  1L  1.5L  50L 0.5L > 50ml litres are larger than millilitres 
Incorrect relationship between millilitres and litres (oversimplification: millilitres are smaller than litres) Students indicate that millilitres are always smaller than litres (this was a very common misconception). This is an over simplification of the relationship between millilitres and litres. It may also relate to not knowing how many millilitres in a litre (below). 
a) b) i) ii) 
5ml  0.75L  1L  1.5L  250ml  1250ml  50L 50ml = 0.5L 100ml is one litre so half is 50ml. 
Incorrect relationship between millilitres and litres (incorrect ratio of ml to L) Students indicate that they do not know how many millilitres in a litre, e.g., there are 100ml (or 10ml, or some other number) in a litre. 
a)  0.75L  1L  1.5L  50L  5ml  250ml  1250ml 
Incorrect relationship between millilitres and litres (indicates that ml > L) Students indicated that millilitres were larger than litres. They may be confused with other measurement units that the suffix makes larger (e.g., km and kg) 
a)  5ml  250ml  0.75L  1250ml  1L  1.5L  50L 
Do not convert 1250ml to litres and order correctly These students correctly ordered the other 6 capacities, but had difficulty converting 1250ml to 1.25L. 
Incorrect relationship between millilitres and litres
Familiarity with millilitre and litre units
Find out how familiar students are with units of measurement for capacity before asking them to put capacities in order. The resources: Throwing a party, How many litres?, Different capacities, and Using orange juice explore working out millilitres and litres with specific containers and could be used to develop students' understanding about how many millilitres make up 1 litre. Having students work by measuring capacity using scales (showing millilitres and litres) may help them to recognise the ratio relationship between the two units.
Developing sense of size
It may also help for students to develop a sense of the size of capacity measures. The resource Millilitres or litres? looks at whether millilitres or litres are the best measure for a range of everyday containers. They could also explore how many of one everyday container fit into another in the resources More or less than a litre and How many millilitres?. The resource How much to fill it? gets students to match up containers to their capacities. If students are uncomfortable using millilitres and litres, they may want to simply look at nonstandard measures, e.g., how many jars fit into this container [Predicting capacity].
Converting millilitre to litres for decimal values:
Cannot convert 1250ml to litres and order correctly
Students who have difficulty converting whole numbers to the decimal fractions and vice versa for working with measurement units could explore the pattern of what happens when a number is multiplied or divided by ten (and powers of ten). They could also work with multiplying decimals to see that decimals work very similarly to whole numbers and ratios (which underlie scales). This may support their understanding of how to move between millilitres and litres. They may also need to explore actual measuring of capacity with measuring jugs and look at the scale to see both millilitres and litres together, for example, the resource How many millilitres? It would help to have a large container (e.g., 2 litres) with a scale of both units.