My classroom seems fine in the morning, but not as comfortable in the afternoon.
Our experience has been that many thermostats are not being operated correctly. While there are several different types of thermostats - some with dials, some with push buttons or arrows - you can adjust 2 degrees up or down.
Example: When you enter your classroom on a cold morning and turn the heat up on the thermostat, it also makes the cooling setpoint higher. Therefore, when it gets warm in the afternoon, your classroom won't be as comfortable unless you turn the thermostat down again.