First assess the seriousness of the situation. Does this teacher just have a style different from what your child is used to, or is she so overburdened or burned out that she's scaring and humiliating her students? Most schools allow parents to observe or volunteer in the classroom. Take what your child says seriously, and find out if there's a real problem.
Then take stock of your child and figure out whether a strict teacher will benefit him or just be hard on him. Some children learn valuable things in adjusting to a teacher's particular style, but children who are timid and afraid may just withdraw and have a difficult year. If you think this is the case with your child, meet with the teacher to see whether she could be more flexible and less scary in her dealings with him. Or think about asking the principal to switch your child to a teacher whose style fits him better.
Set up special times at home when you play school with your child, alone or with a couple of his friends, with your child as the teacher and you as the student. Your child can use this opportunity to show you in playful ways what's going on in school. When he is in the more powerful position, he will feel safe to laugh or cry or talk about it.
Alternatively, you could gather a few children who are having difficulty with a strict teacher and play the teacher yourself. Encourage the children to band together and say to you all the things they want to say to
the teacher, or hold you (standing in for the teacher) down, or tell you that you shouldn't scare your students. You can do a lot with play that will help your child release his feelings about school; this will help him think productively about how to deal with the teacher.
A teacher who is dealing with 20 to 30 kids in a classroom may have no idea, particularly with a very scared child, that something is wrong. In this case, a meeting among the three of you may help. One of my sons was scared of his teacher; we met with her and he was able to tell her, with my backing, what she was doing that he liked and what scared him. Some teachers do well with such talks, but others don't have the patience or time.
If your child is getting into trouble all the time, he may be scared of his teacher and dealing with it by standing up to her or acting as if he doesn't care about her rules. In that case a teacher can easily lose track of a child's emotional state. You can help the teacher by giving her a sense of what's going on with your child. Your child can also have a private session with the teacher to devise a signal, such as a tap on the shoulder, that the teacher can use to let him know when he's getting out of line without embarrassing him in front of the class. If your child gets to be part of the team devising a solution, it can help him feel more powerful.