I was nearly 11 when we decimalised our currency. We couldn't carry on using shillings and half crowns because they were taken away, so we had to get used to the new money. Even if Penny Arrows more than doubled in price overnight. ( only 100 penny arrows for a quid, whereas you could get 240 of them for the same quid the day before, and the sweet shop man had bought them at imperial rate.)
Weights and measures were taught to us by old teachers who didn't use the new metrics, didn't understand them and didn't want to. We never learned it properly. Tape measures, rulers, scales were still produced with imperial units. Unlike the money, people could - and did - carry on using cubits and spans feet and inches, pints and miles.
Take them away and the next generation will be fluent in millimetres, litres and kilos.