The previous blackboards were almost all black. In the long-term use, schools and teachers found that the black-and-white contrast of wooden boards was too strong. The students looked at it for a long time, and their eyes were very tired, which affected their eyesight. Moreover, when the outside light is strong, the blackboard is particularly easy to reflect light, so that students sitting on both sides can see the words on the blackboard, so the school slowly changed the black blackboard into dark green, which can protect hyperopia instead of reflecting light.

In fact, the blackboard has undergone many changes since its birth. The first board is usually made by painting the board black or coating the smooth surface with walls and black pigments. These two types of blackboards are easy to manufacture and cheap, but they are not durable and have a short shelf life. At that time, we were still poor and could do it, and we didn't think much.

Later, with the improvement of the whole social and economic level, some schools replaced the old blackboards with frosted glass boards. However, due to fragility, dust and transportation difficulties, this kind of board quietly and slowly withdrew from the market. At present, the blackboards are basically colored steel plates or composite plates, which are durable, will not drop or fade, and have a good writing feeling and clear handwriting.

Our country has always attached great importance to education. Today, the situation of most schools in China is completely different from that of 20 years ago. There is heating in winter, air conditioning in summer, and even some dormitories in the school. Compared with before, the restaurant has also undergone great changes. In the 1980s, the canteen was full of radishes, cabbages and melons, which was very annoying to eat. However, in today's canteen, all kinds of dishes are dazzling and inexpensive.