No principal and no superintendent should allow a class of 28 third-grade students anywhere for any reason. There is no way for a teacher to be able to tell who is behind in reading or math. There is no way for a teacher to be able to set a path and lift a student up when there are 28 in a classroom. There is no way for a teacher to keep the class of 27 or 25 or 18 students quietly working on task while helping that one student or three students or 10 students who need individualized help.
Third grade is a pivotal year for reading and mathematics.
Proficiency is expected at this level. Superficial covering of these topics will never result in mastering that is necessary to build on in later grades. A teacher who spends half a day trying to get third-graders in their seats is not achieving the goals that will have disastrous consequences later on if they are not met. The picture shows students quietly sitting still for a photograph. You can bet that is not the way 28 third-graders behave in their classroom.