Public Schools - Disadvantages

Very high expectations of a first year teacher

Typically, once a public school teacher has taught a few years, they can't be fired because teachers unions specify that layoffs happen by seniority (i.e. in cutbacks, the newest people go first) rather than by ability. Thus, a principal's only chance to get rid of bad teachers is in the probationary year or years of their employment. For this reason, if you appear to be borderline (i.e. you're getting better at teaching, but it's uncertain how far you'll improve), principals are inclined to fire you outright or tranfer you to another school so they won't get stuck with you. In other words, the best performance and highest standards are expected right at the beginning, when you're still trying to figure out what the heck is going on.

New teachers often get the worst courses, schedules, and students in the school. This is also due to the seniority system. The more senior teachers make sure they're teaching the easiest classes (i.e. students at well-behaved ages, electives that students pick or are screened for) to reduce their workload. This means that the new teacher gets the courses nobody wants (i.e. where the students are particularly heterogenous in interest, background, and ability and are more rambunctious and rebellious (grades 5 through 9)) and where the scheduling is tough (i.e. running all over the school, teaching a hodgepodge of classes with many different preps in different classrooms).

There's no entrance test for public school. No one screens out students who happen to be destructive or uninterested. You have to deal with some of the most challenging kids. Often, due to integration, it's difficult because there are so many differences in terms of interest, ability, special needs, etc. It requires much more skill and prepatory work to teach a heterogeneous rather than a relatively homogenous class.