New endoscopists require a large volume of expert-proctored colonoscopies to attain minimal competency. Developing multi-fingered, synchronized control of a colonoscope requires significant time and exposure to the device. Current training methods inhibit this development by relying on tool hand-off for expert demonstrations. There is a need for colonoscopy training tools that enable in-hand expert guidance in real-time. We present a new concept of a tandem training system that uses a telemanipulated preceptor colonoscope to guide novice users as they perform a colonoscopy. This system is capable of dual-control and can automatically toggle between expert and novice control of a standard colonoscope's angulation control wheels. Preliminary results from a user study with novice and expert users show the effectiveness of this device as a skill acquisition tool. We believe that this device has the potential to accelerate skill acquisition for colonoscopy and, in the future, enable individualized instruction and responsive teaching through bidirectional actuation.