The Danielson model of classroom observation, which breaks the evaluation into the domains of planning and preparation, classroom environment, instruction and professional responsibilities, is a good starting point for preparing a checklist for an observation. The first three domains are most relevant to the activities that should happen in a good classroom on a daily basis.
The first domain is planning and preparation, which references the lesson plan. One item to add to a checklist for this domain are standards: has the teacher referenced the appropriate state and Common Core standards that align to the lesson? The activities and assessments for the lesson should be based around a set of instructional outcomes, or learning goals.
The second domain covers the classroom environment, including the physical layout of the room. For example, are desks in rows or in small groupings, and for what purpose? An observer might also look to see if there are examples of student work hanging up around the room. A teacher must demonstrate that she can manage student behavior and that classroom procedures, such as how to hand in work, are understood by all students.
The third domain, instruction, assesses the actual lesson. The observer evaluates how the teacher communicates with students, what questioning and discussion techniques are used and whether students are engaged in learning. The teacher must show flexibility in her instruction to meet the needs of all learners, and students must be assessed on the learning goals, either formally or informally, before they leave the classroom.
The final domain is not as applicable to the in-class observation. It assesses a teacher's professionalism and is often addressed in a final evaluation for the school year. However, a teacher should be sure to dress and act professionally during a classroom observation.