As a parent, I have found the use of green lenses to be nothing short of miraculous (albeit with eye and listening exercises as DS has a diagnosis of auditory processing disorder as well as visual). He went from unable to read for more than 10 minutes, struggling to decide text to reading Harry Potter in about 2months. (This is not a discussion about the literary merits of HP!).
DS described text as smooching and stretching without his glasses and finds reading very hard work. With glasses, he happily reads history/ politics books for hours.
We bought green paper and books to use at school, but now he wears the glasses he doesn’t need them. They were useful at the start when he used overlays.
At school, I never use a white board with black text. Mine is usually grey as I have two children who use different colours. When I have one child using an overlay, I’ll turn the board their colour. When helpful, I’ll produce books/ worksheets etc in the right shade and I’ll check we have the right colour put aside for SATs.
However, many children come in with overlays and never use them, so I wonder how helpful they actually are. I had one who had a report which said no direct light, but not too dark, not near a window, in direct line with the board, but avoid the glare. I sent photos of my room to the assessor and asked where I should sit the child. They had to admit that their instructions made it a little challenging (impossible).
I’d advise you to buy overlays not glasses at first. The colour they need can change over time, especially if they have exercises to do as well. The glasses are a lot more expensive to change.