I had this displayed each year in my class. Sometimes I used the mini traffic lights to start with and then once children understood moved onto coloured dots only. Some children remained on the preprinted lights as they needed the layout to choose the correct circle and some needed the visual. I always had 1 lesson on the traffic light system to explain each colour. Some children needed the yellow explaining as needing more practice to get it right rather than just more practise to feel confident as self-confidence sometimes affected this result. It also needed explaining that red means you cannot do it without help...rather than if I had any help I am red as sometimes 2 minutes extra help meant a child could be green - which is just good teaching practise.