A good letter should address that. A letter from a principal holds the most weight for me, but a letter from a parent whose child had the teacher can also be very nice. In letters of recommendation, I feel it is important to include how well the applicant works with others. I believe that one of the most important skills a new teacher can have is that of classroom management and discipline. The letter of recommendation should illustrate how the student teacher employed a good classroom management scheme.
Organization is also a skill necessary for success in the first years of teaching.
How the student teacher handled the time in the classroom effectively should also be spoken of in the letter. Today, most administrators want to know that the teacher can use technology successfully with students. Letters of recommendation should list specific examples of the candidate's strong points.