Make a note of the physical size of the classroom. This includes whether there is enough space for all students, or if some of them are cramped uncomfortably into corners or wherever there is space. There should be enough room for desks and chairs for everyone. Also consider the size of the class when it comes to the number of students, and whether there are too many for the teacher to handle. Thirty students to one teacher is a lot -- a better ratio would be 20 to 25 students per teacher.
Another item on your checklist should be academic materials, including books, pens, paper and other supplies. Determine whether there are enough for every student or if students sometimes have to share. If special equipment is needed - for example, for handicapped students - it should be in the classroom, or easily retrievable if it is not.
The teacher's attitude toward the children should also be considered, as well as her feelings about parental observation. She should welcome parents into the classroom, provided that doing so does not interrupt academics. Watch the teacher's interactions with students -- he should be patient when handling questions and discipline problems. Observe the students' attitude toward the teacher -- if the teacher feels positively toward them, such feelings are often reflected back by the children.
Check to see if the students are involved in their schoolwork. There should be a relaxed but disciplined atmosphere in which students are happily busy with their tasks. Watch out for frequent outbursts, violent displays and temper tantrums. Also observe whether the children seem bored or listless -- while they may not be enthusiastic about every subject, the teacher should keep them energized enough to pay attention to the material.
Finally, observe whether the environment is comfortable and safe for everyone in the classroom. It should be well-insulated and heated during winter, and cool during summer (either through the use of fans or air conditioning). Watch out for cracks in walls or floors, peeling paint and other safety hazards that could endanger your children.