Complaints about incompetent teachers are a form of self-hypnosis, spread by the parents of slow-learning children, much like the clucking of soldier's mothers who are afraid to send their talentless, lazy sons into the army, fearing they will return as invalids. When a fifth-grader has to explain, step by step, why the area of a large rectangle can be calculated by multiplying the area of the small rectangles that make it up by their number, and still half or a third of the students don't understand, even though they aren't playing on their phones but are genuinely trying to grasp the concept, it's sad. Just as it is to hire a tutor to explain equations with one variable or to have a child read syllables up to the seventh grade.
Children are not guinea pigs that you can throw a cabbage at and hang a bottle for them, and then rightfully blame the education system.