What Belgian schools mean by « grandeurs » — and why conversions trip children up
« Grandeurs » is the Belgian curriculum's word for measurement: lengths, masses, capacities, areas, perimeters, volumes and durations, plus converting between their units. It is its own booklet in the CEB, and conversions are where children lose the most marks — usually by moving the decimal comma one place too few.
What the booklet actually covers
If you were schooled in an English-speaking system, « grandeurs » has no exact equivalent. It is broader than "measurement" as a topic and narrower than "maths": it groups together everything about quantities that can be measured, and the arithmetic that goes with them.
- Lengths, masses and capacities, and the metric ladder between their units
- Perimeter, area and volume of the usual shapes and solids
- Durations: reading timetables, adding times, working across the hour
- Money, expressed with a decimal comma: 4,50 € not €4.50
Why conversions cost so many marks
A conversion error rarely stays local. If a child turns 2,5 L into 25 cL instead of 250 cL, every later step of the problem is wrong even though the reasoning was sound. One slip, several marks.
The slip itself is almost always the same: moving the comma one rank instead of two. Litres to centilitres is two ranks, because « centi » means a hundredth. Children who move it once are thinking of millilitres, or of the previous exercise.
The method Belgian classrooms use
Children here are taught a positional ladder rather than a formula. It is worth knowing, because helping with a different method is how homework turns into an argument.
- Write the units in order, from big to small: kL, hL, daL, L, dL, cL, mL.
- Count the steps from the unit you have to the unit you want. Litre to centilitre is two steps to the right.
- Move the comma the same number of places, in the same direction: 2,5 becomes 250.
How to help without confusing them
Ask your child to show you the ladder before they compute anything. If they cannot draw it, the problem is the ladder, not the sum. Then check the direction: converting to a smaller unit always gives a bigger number. That single sanity check catches most errors, and it is one your child can learn to run alone.
Does this appear in the CEB?
Yes — « Grandeurs » is one of the CEB's own booklets, and conversions also appear inside the problem-solving booklet, where they are worth more because the rest of the answer depends on them.
Practising it
Hopla6 explains every wrong answer in three steps, in the language of your child's school, and gives your dashboard in English so you can follow without translating. Free during launch.
Frequently asked
My child is in a French-language school but we speak English at home. Can I still help?
Yes, provided you use the method taught in class rather than the one you learned. The ladder above is that method. Where you are unsure, ask your child to explain it to you — being made to explain is itself good revision.
Is the CEB taken in Dutch-language schools too?
No. The CEB is the certificate for French-language schools in the Fédération Wallonie-Bruxelles. Dutch-language schools in Flanders and Brussels sit the Vlaamse toetsen instead, which are diagnostic central tests rather than a pass-or-fail certificate.
Should I buy a conversion chart to stick on the fridge?
It helps far less than having your child draw the ladder themselves each time. The drawing is the skill; the chart replaces it.