When planning to teach with web-based materials in a computer lab, it is critical that the instructor "test-drive" the lesson in the lab before the class, with computer support staff available if possible. While testing the material you will cover in class, make sure of the following:
It often helps to photocopy the lesson steps for each student, and for the whole class to go over the main points before the students start using the computers. While the students are engaged in the activity circulate to make sure none are lost or off-track.
When planning to use a computer lab for the first time, assess your students' computer experience or competence beforehand and if possible pair less experienced users with more experienced ones. Whenever possible, rely on more tech savvy students to help peers who are more tech-challenged. It is not a good use of an instructor's time to trouble shoot every minor tech problem when students can do this. Having students work individually, in pairs, or in small groups can all work. It is usually best to have students work out any problems for themselves rather than to try to follow along with the instructor at a computer.
When conducting a face-to-face discussion in class, have students turn off the monitors. Computers are necessary for online tasks and interaction, but a horrible distraction when trying to facilitate in-class, synchronous discussion
And most importantly, have a back-up plan in case the technology fails! It is not unusual for Internet servers or school networks to be out of service. So even if you checked everything the day before and it worked, it may not work at the time of your class. So always be prepared with an alternate plan.