In this article, we present the design and operation process of the AssIuT-IoT testbed; an educational and remotely accessible testbed for Internet-of-Things (IoT) applications. The testbed adopts the experiment as a service (EaaS) model in which users are able to access the testbeds and reserve/use the available resources remotely over the Internet. Also, the testbed is federated with other ones distributed among different locations to allow the sharing of resources, user accounts, and policies. The federated testbeds form an educational consortium that facilitates students' access to hardware resources available at different locations. AssIuT-IoT testbed consists of a control server and a set of IoT nodes (hardware resources) supported with different wireless communication capabilities. We present the design, operation, and performance details of the testbed in terms of the hardware and software components. We describe the steps needed to complete experiments using our testbed and we provide some examples. Moreover, we evaluate the testbed and the IoT network's performance. Finally, we present the IoT students' competition as one of the activities where the testbed has been used.