Mr. grimshaw uses frequent questioning of students, calling on those who raise their hands to respond. your textbook author would evaluate this procedure as:

If these were the choices:
A) effective, because it treats all students equally across a wide range of ability. 
B) limited, because students who do not volunteer will escape having to respond. 
C) effective, because it avoids having to call on people and possibly embarrassing them. 
D) effective, because volunteers usually give correct responses.

My answer would be: 
B) limited, because students who do not volunteer will escape having to respond. 

When teachers only call for students raising their hands to answer your questions, it limits the ability of the teacher to determine the learning level of the students in the classroom. Teachers must also call on students who do not raise their hands so that students will be more motivated to learn if their chances of being called in class are more probable.