The invention discloses a counter balance for middle school teaching. The counter balance comprises a base and vertical support arms. Insert holes are formed in the upper surface of the base. The bottom portion of each vertical support arm is provided with a first magnet. A rotating disk fixedly inserted to a fulcrum shaft is arranged under each insert hole. The outer circle side wall of each rotating disk is provided with a plurality of convex teeth. Second magnets and third magnets are arranged alternately on the plurality of convex teeth. The second magnet and one end of a first magnet areopposite poles, and the third magnet and one end of the first magnet are same poles. A through hole is formed in the bottom portion of the insert hole. An external thread is formed on the outer wall of each vertical support arm. An adjusting gear pressed against the upper surface of the base is screwed in each vertical support arm. One side of each adjusting gear is engaged with a horizontal toothbar. The two adjusting gears at the two sides of the base are engaged to the two sides of the tooth bar respectively. A placement groove is formed in the upper surface of the base. The tooth bars areinserted into the placement groove. The two-end inner walls of the placement groove are respectively provided with a magnet layer. The two ends of the tooth bar are respectively provided with an ironlayer. The counter balance can effectively protect edges when placed.