Not all checkpoints have space for a dedicated precheck lane. Some larger airports have dedicated precheck checkpoints, others have a dedicated lane at the checkpoint. Others have no precheck lane, causing slight differences in the processing of people with precheck.
From what I've seen at these checkpoints, the person checking ID/boarding pass calls back to the person gate keeping the metal detector that they have a precheck. They keep shoes on and go through the metal detector, but the screening for the baggage xray is different depending on whoever is the manager on duty at the time.