Pay is a huge one, but also the lack of additional supports for special needs has made teaching terrible. I know several teachers that quit because they struggled with dealing with difficult kids in the classroom that could have been dealt with by having aids or additional options to support those students. Instead, they just put them in the class and expect the teacher to have the normal classwork, plus modified classwork to address special needs, and be able to provide everyone the amount of support they need. Add in frustrated parents and politics and the pay becomes 5x too little.